A method is provided for efficiently removing the silicon substituent which protects the 3'-hydroxyl group and the 5'-hydroxyl group of a ribose of a ribonucleic acid derivative in which the 2'-hydroxyl group of the ribose is protected with the following substituent (I) ##STR00001## where WG1 represents an electron withdrawing group, and the 3'-hydroxyl group and the 5'-hydroxyl group of the ribose are protected with a silyl protecting group.