The present invention provides a process for producing an encapsulating material for solar cell which makes high-speed crosslinking possible and causes no blister phenomenon without significant restrictions being imposed on the conditions for molding the encapsulating material.The present invention provides a process for producing the encapsulating material for solar cell including impregnating a molded form of an ethylene copolymer with an organic peroxide in a liquid state at normal temperature which shows a decomposition temperature (a temperature at which the half-life period is one hour) of not higher than 150° C.A process for producing the encapsulating material for solar cell in which dialkyl peroxide (A) and an organic peroxide (B) selected from peroxycarbonate and peroxyketal at a ratio by weight of 10/90 to 90/10 of (A) and (B) in a liquid state impregnate the molded form of the ethylene copolymer is a preferable embodiment of the present invention.