Invest in Small Business Act of 2009 - Amends the Internal Revenue Code to: (1) increase the exclusion from gross income of gain from the sale or exchange of qualified small business stock from 50 to 100 % of such gain and to reduce the required holding period for such stock from five to four years; (2) deny a tax exclusion for small business stock held by a 25% controlled corporate group; (3) repeal as an item of tax preference under the alternative minimum tax the exclusion of gain from the sale of small business stock; (4) repeal the 28% income tax rate on the gain from the sale of small business stock which is not excluded from gross income; (5) revise the definition of "qualified small business" for certain tax purposes to mean a C corporation with aggregate gross assets not exceeding $100 million (currently, $50 million); and (6) provide for an annual inflation adjustment to the small business aggregate gross asset amount after 2009.