NOVELTY - A resin composition comprises an ethylene- alpha -olefin copolymer, an organic peroxide, and a silane coupling agent. The copolymer has a density of 0.86-0.92 g/cm3, a ratio of 8 or less with respect to Z average molecular weight and number average molecular weight, a melt viscosity of 1.2x 105 poise or more at a shear rate of 2.43x 10 second-1 and 100 degrees C, a melt viscosity of 2x 104 poise or more at a shear rate of 2.43x 102 second-1 and 100 degrees C, and a branch number (N) of (-0.67E+53) or more by comonomer in polymer.    USE - Resin composition is used for sealing materials of thin-film solar cells or solar cell using glass plates as substrates used in solar-cell modules (all claimed). Can also be used for manufacturing water barrier sheets and tarpaulin.    ADVANTAGE - The resin composition has excellent heat resistance, transparency, softness, and balance between rigidity and crosslinking efficiency. The resin composition enables economical manufacture of solar-cell modules having excellent transparency, flexibility, durability, weather resistance, and conversion efficiency.    DETAILED DESCRIPTION - A resin composition comprises an ethylene- alpha -olefin copolymer, an organic peroxide, and a silane coupling agent. The copolymer has a density of 0.86-0.92 g/cm3, a ratio of 8 or less with respect to Z average molecular weight and number average molecular weight measured by gel permeation chromatography, a melt viscosity of 1.2x 105 poise or more at a shear rate of 2.43x 10 second-1 and 100 degrees C, a melt viscosity of 2x 104 poise or more at a shear rate of 2.43x 102 second-1 and 100 degrees C, and a branch number (N) of (-0.67E+53) or more by comonomer in polymer, where N is branch number per carbon number of a total of 1000 principal chains and side chains as measured by NMR, and E is tensile elasticity modulus of a sheet measured by ISO1184-1983. An INDEPENDENT CLAIM is included for solar-cell sealing material formed by pelletizing or forming the resin composition into a sheet.