An encapsulating material for solar cell comprising: an ethylene/a-olefin copolymer; and an organic peroxide having a one-minute half-life temperature in a range of 100°C to 170°C, wherein a complex viscosity of the encapsulating material for solar cell, which is measured through solid viscoelasticity measurement under conditions of a measurement temperature range of 25°C to 150°C, a frequency of 1.0 Hz, a rate of temperature increase of 10°C/minute, and a shear mode, has a minimum value (η *1 ) of the complex viscosity at a temperature in a range of 100°C to lower than 135°C, the minimum value (η *1 ) of the complex viscosity is in a range of 7.0×10 3 Pa·s to 4.0×10 4 Pa·s, the complex viscosity (η *2 ) of the encapsulating material for solar cell at 150°C is in a range of 2.0×10 4 Pa·s to 1.0×10 5 Pa·s, and a content of the organic peroxide in the encapsulating material for solar cell is in a range of 0.1 parts by weight to 3 parts by weight with respect to 100 parts by weight of the ethylene/a-olefin copolymer, wherein the ethylene/a-olefin copolymer satisfies the following requirements a1) and a2): a1) a content ratio of a structural unit derived from ethylene is in a range of 80 mol% to 88 mol%, and a content ratio of a structural unit derived from an α-olefin having 3 to 20 carbon atoms is in a range of 12 mol% to 20 mol% (here, a sum of the structural unit derived from ethylene and the structural unit derived from the α-olefin is 100 mol%); a2) MFR, which is based on ASTM D1238 and measured under conditions of a temperature of 190°C and a load of 2.16 kg, is in a range of equal to or more than 0.1 g/10 minutes and less than 2.0 g/10 minutes. an ethylene/a-olefin copolymer; and an organic peroxide having a one-minute half-life temperature in a range of 100°C to 170°C, wherein a complex viscosity of the encapsulating material for solar cell, which is measured through solid viscoelasticity measurement under conditions of a measurement temperature range of 25°C to 150°C, a frequency of 1.0 Hz, a rate of temperature increase of 10°C/minute, and a shear mode, has a minimum value (η *1 ) of the complex viscosity at a temperature in a range of 100°C to lower than 135°C, the minimum value (η *1 ) of the complex viscosity is in a range of 7.0×10 3 Pa·s to 4.0×10 4 Pa·s, the complex viscosity (η *2 ) of the encapsulating material for solar cell at 150°C is in a range of 2.0×10 4 Pa·s to 1.0×10 5 Pa·s, and a content of the organic peroxide in the encapsulating material for solar cell is in a range of 0.1 parts by weight to 3 parts by weight with respect to 100 parts by weight of the ethylene/a-olefin copolymer, wherein the ethylene/a-olefin copolymer satisfies the following requirements a1) and a2): a1) a content ratio of a structural unit derived from ethylene is in a range of 80 mol% to 88 mol%, and a content ratio of a structural unit derived from an α-olefin having 3 to 20 carbon atoms is in a range of 12 mol% to 20 mol% (here, a sum of the structural unit derived from ethylene and the structural unit derived from the α-olefin is 100 mol%); a2) MFR, which is based on ASTM D1238 and measured under conditions of a temperature of 190°C and a load of 2.16 kg, is in a range of equal to or more than 0.1 g/10 minutes and less than 2.0 g/10 minutes. a1) a content ratio of a structural unit derived from ethylene is in a range of 80 mol% to 88 mol%, and a content ratio of a structural unit derived from an α-olefin having 3 to 20 carbon atoms is in a range of 12 mol% to 20 mol% (here, a sum of the structural unit derived from ethylene and the structural unit derived from the α-olefin is 100 mol%); a2) MFR, which is based on ASTM D1238 and measured under conditions of a temperature of 190°C and a load of 2.16 kg, is in a range of equal to or more than 0.1 g/10 minutes and less than 2.0 g/10 minutes. <EOS>