The present invention relates to a process for producing a resin composition for an optical semiconductor from a powdery material and a liquid material using a kneader having a first supply port and a secondary supply port disposed at a downstream side of the first supply port, the process including: a step of supplying the powdery material into the kneader from the first supply port and delivering the powdery material to a second supply port side by the kneader at a temperature at which the powdery material is not melted; a step of melting the powdery material by heating and simultaneously supplying the liquid material from the second supply port under a pressure higher than a pressure in the kneader to knead a melted product of the powdery material and the liquid material; and a step of further kneading a kneaded product thereof while cooling.