Provided is a novel production method for producing silicon clathrate II. In the production method for producing silicon clathrate II, in a reaction system in which a Na—Si alloy containing Na and Si and an Na getter agent coexist so as not to be in contact with each other, the Na—Si alloy is heated and Na evaporated from the Na—Si alloy is thus caused to react with the Na getter agent to reduce an amount of Na in the Na—Si alloy.