To provide a structural cured polysiloxane which can be prepared by curing at room temperature without adding a catalyst, at a low cost and with ease.

This method comprises obtaining a polysiloxane product composed mainly of linear structure components by a partial blocking reaction of a polysiloxane formed by hydrolysis of an alkoxysilane, with phosphoric acid or a phosphoric ester group; adding a filler to the polysiloxane product followed by mixing; and curing at room temperature without adding a catalyst. It is especially preferred that 100 pts.wt. polysiloxane product composed mainly of linear structure components which are blocked with phosphoric acid or a phosphoric ester group is mixed with 1 to 100 pts.wt. filler; the resultant mixture is cured in a mold by allowing to stand at room temperature without adding a catalyst; and the mold is removed after 1 to 3 days.