A method for producing a molecular compound which comprises mixing and kneading a solid host compound and a solid or liquid guest compound by using a kneader and optionally followed by extruding and granulating, wherein the method further comprises one or more of the steps of holding the product at a temperature which is 50.degree. C. or higher and not higher than the emission temperature for the guest compound, washing the formed molecular compound with a solvent capable of dissolving the guest compound, pulverizing in advance the solid host compound, and adding a poor solvent such as water prior to mixing and kneading. The method allows the production of a molecular compound having improved stability.