Exhibit 23.1

            CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the reference to our firm under the caption "Experts" and to the
use of our report dated March 25, 2004 (except for Note 15, as to which the date
is April 15, 2004) in Amendment No. 2 to the Registration Statement on Form S-1
(No. 333-114735) and related Prospectus of Nanosys, Inc. for the registration of
shares of its common stock.

                                                           /s/ Ernst & Young LLP

Palo Alto, California
May 25, 2004