The present invention relates to a pressure-sensitive adhesive composition including a polymer of a monomer mixture containing isobornyl (meth)acrylate, a pressure-sensitive adhesive sheet, and a semiconductor wafer backgrinding method. In the present invention, by using isobornyl (meth)acrylate which is a hard-type monomer and has a low hydrophilic property, a pressure-sensitive adhesive composition having superior releasing and re-releasing properties and wettability with respect to the wafer, and having an excellent wafer-proofing property; a pressure-sensitive adhesive sheet prepared by using the pressure-sensitive adhesive composition; and a backgrinding method using the pressure-sensitive adhesive sheet can be provided.