10-Q/A

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 10-Q/A

Amendment No. 1

(Mark One)

þ Quarterly Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

For the quarterly period ended December 31, 2005

OR

o Transition Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Commission File Number 1-9965

KEITHLEY INSTRUMENTS, INC.

(Exact name of registrant as specified in its charter)

Ohio
(State or other jurisdiction of incorporation or organization) 34-0794417
(I.R.S. Employer Identification No.)

28775 Aurora Road, Solon, Ohio 44139
(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code: (440) 248-0400

     Indicate by check mark whether the Registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

YES þ   NO o

     Indicate by check whether the registrant is a large accelerated file, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer and large accelerated file” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer o   Accelerated filer þ   Non-accelerated filer o

Indicate by check whether the registrant is a shell Company (as defined in Rule 12b-2 of the Exchange Act).

YES o   NO þ

     As of February 1, 2006 there were outstanding 14,338,176 Common Shares, without par value and 2,150,502 Class B Common Shares, without par value.

Explanatory Note

This Amendment No. 1 to our quarter Report on Form 10-Q/A amends our certifications filed as Exhibits 31(a) and 31(b) by Joseph P. Keithley and Mark J. Plush pursuant to Rule 13a-14(a)-15d-14(a) for the quarterly period ended December 31, 2005, originally filed on February 9, 2006 (the “Original Filing”). We are filing this Amendment No. 1 to include the language underlined in the text below, which was inadvertently omitted from the Original Filing:

The registrant’s other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

This Amendment No. 1 does not affect any other information contained in the Original Filing.

Item 6. Exhibits.

             (a) Exhibits. The following exhibits are filed herewith:

Exhibit
Number	Exhibit
31(a)	Certification of Joseph P. Keithley pursuant to Rule 13a-14(a)-15d-14(a).
31(b)	Certification of Mark J. Plush pursuant to Rule 13a-14(a)-15d-14(a).

1

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

	KEITHLEY INSTRUMENTS, INC. (Registrant)
Date: March 10, 2006	/s/ Joseph P. Keithley
	Joseph P. Keithley
	Chairman, President and Chief Executive Officer (Principal Executive Officer)

Date: March 10, 2006	/s/ Mark J. Plush
	Mark J. Plush
	Vice President and Chief Financial Officer (Principal Financial and Accounting Officer)

2

EX-31.1

Exhibit 31(a)

Certification Pursuant to Rule 13a-14(a)/15d-14(a)

I, Joseph P. Keithley, certify that:

1.	I have reviewed this quarterly report on Form 10-Q of Keithley Instruments, Inc.;
2.	Based on my knowledge, this quarterly report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this quarterly report;
3.	The registrant’s other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)	designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this quarterly report is being prepared;
b)	designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;
c)	evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this quarterly report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this quarterly report based on such evaluation; and
d)	disclosed in this quarterly report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

4. The registrant’s other certifying officers and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)	all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and
b)	any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: March 10, 2006	/s/ Joseph P. Keithley
	Chairman, President and Chief Executive Officer

EX-31.2

Exhibit 31(b)

Certification Pursuant to Rule 13a-14(a)/15d-14(a)

I, Mark J. Plush, certify that:

1.	I have reviewed this quarterly report on Form 10-Q of Keithley Instruments, Inc.;
2.	Based on my knowledge, this quarterly report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this quarterly report;
3.	The registrant’s other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have:

a)	designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this quarterly report is being prepared;
b)	designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;
c)	evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this quarterly report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this quarterly report based on such evaluation; and
d)	disclosed in this quarterly report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

4. The registrant’s other certifying officers and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

a)	all significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and
b)	any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

Date: March 10, 2006	/s/ Mark J. Plush
	Vice President and Chief Financial Officer