Disclosed i s a novel nucleic acid molecule capable 0 1 suppressing expression 0 1 a gene and capable o f e ncient manufacture. The single-strand nucleic acid molecule contains an expression suppression sequence that inhibits of a target gene, and contains, i n order fi"om the 5 end t o the 3 end, a 5 end region (Xc), an inner region (Z) and a 3 (Yc), wherein the inner region (Z) i s constituted b y linking an inner 5 end region (X) and an inner 3 end region (Y), the gion (Xc) i s complementary t o the inner 5 end region (X), the 3 end region (Yc) i s complementary t o the inner 3 end and at least one o f the inner region (Z), the 5 end region and the 3 end region includes the aforementioned expression s sequence. B y means o f this single-strand nucleic acid molecule, expression o f the target gene can be suppressed.
