To provide a method of manufacturing a sealing sheet for a solar cell, in which uniform impregnation with organic peroxide is obtained to achieve uniform crosslinking, and no fish eye is generated.

In the method of manufacturing the sealing sheet for the solar cell, organic peroxide containing pellets are manufactured by supplying ethylene copolymer pellets and liquid organic peroxide of ≥100°C in one-hour half-life temperature into a rotary container, and rotating the rotary container while heating the ethylene copolymer pellets at 25 to 45°C to impregnate the ethylene copolymer pellets with the organic peroxide, and the organic peroxide containing pellets are supplied to an extruder to be fused and kneaded, and then extruded from the extruder, thereby manufacturing the sealing sheet.