Exhibit 23   Consent of Independent Registered Public Accounting Firm   We consent to incorporation by reference in the Registration Statements (Form S-8 No. 333-30528) of our report dated June 28, 2010 relating to the statements of net assets available for benefits of the Sigma-Aldrich Corporation 401(k) Retirement Savings Plan as of December 31, 2009 and 2008, the related statements of changes in net assets available for benefits for the years then ended, and the related supplemental schedule of Schedule H, line 4i- schedule of assets (held at end of year) as of December 31, 2009, which appears in the December 31, 2009 annual report on Form 11-K of the Sigma-Aldrich Corporation 401(k) Retirement Savings Plan.     St. Louis, Missouri June 28, 2010