To provide an activation method for a crystalline titanosilicate catalyst with an MWW structure which can efficiently activate the catalyst.

The activation method for the crystalline titanosilicate catalyst with the MWW structure treats the catalyst using a silylating agent. As its preferable examples, following cases can be cited; when the catalyst is used for epoxidation of an olefin by hydrogen peroxide, and hydroxylation of benzene or a phenolic compound by hydrogen peroxide, when the catalyst is used for epoxidation of propylene by hydrogen peroxide, when the catalyst is used for a reaction using a nitrile compound as a solvent, when Ti (titanium) is introduced into the catalyst at the crystallization of the crystalline titanosilicate catalyst with the MWW structure, or the like.