An object of the present invention is to provide a composition for suppressing expression of a target gene, and the like. A composition comprising an RNA-encapsulated liposome, wherein the RNA contains a sequence consisting of 15 to 30 contiguous bases of a target gene mRNA (hereinafter, sequence X) and a base sequence (hereinafter, complementary sequence X') complementary to the sequence X, 1 to 90% of all sugars binding to the bases of the sequence X and the complementary sequence X' being ribose substituted by a modifying group at 2' position, and the liposome being capable of reaching a tissue or an organ containing an expression site of the target gene is provide.