A resin composition for a solar cell encapsulant is provided, containing an ethylene•α-olefin copolymer and an organic peroxide or a silane coupling agent or the like, and having superior heat resistance, transparency, flexibility and adhesion property to a glass substrate, as well as good balance between rigidity and cross-linking efficiency, as well as a solar cell encapsulant, and a solar cell module using the same. The resin composition has an ethylene•α-olefin copolymer (A), having the characteristics (a1) to (a4), along with characteristics (a5) or (a6), and an organic peroxide (B) and/or a silane coupling agent (C).