Proton decay is studied in supersymmetric grand unified models. Supersymmetry combined with SU(3)×SU(2)×U(1) at low energies allow in general ΔB ≠ 0 operators of dimension five as well as four which involve scalar partners of quarks. It is argued that these operators should be forbidden by imposing selection rules. For ΔB ≠ 0 supersymmetric operators of dimension six which contain four-fermion interactions, only two types are allowed by supersymmetry.