Back sheet for solar cell and solar cell module employing the same

A back sheet for solar cells which is composed of superposed layers comprising a weatherable resin layer (1), a water-vapor-barrier layer (2), an adhesive layer (3), and a plastic film (4); and a solar cell module employing the back sheet. The weatherable resin layer (1) is obtained from a resin composition comprising: a vinyl copolymer (A) obtained by grafting a polyester to a copolymer obtained from monomers including an unsaturated dibasic acid as an essential ingredient; a polyisocyanate compound (B); and a polyester (C). The back sheet for solar cells is inexpensive and has excellent long-term outdoor weatherability.