A cell-penetrating peptide described in any of (A) to (D) below gives cell membrane permeability and further transmucosal absorbability to a physiologically active substance: (A) a peptide having the amino acid sequence represented by SEQ ID NO:1； (B) a peptide having an amino acid sequence which is the same as the amino acid sequence represented by SEQ ID NO:1 except that one or several basic amino acids are substituted, deleted, inserted and/or added, which peptide has cell membrane permeability； (C) a peptide having an amino acid sequence which is the same as the amino acid sequence represented by SEQ ID NO:1 except that 1 to 5 amino acids are substituted, deleted, inserted and/or added, which peptide has cell membrane permeability； (D) a peptide having: an amino acid sequence represented by the reverse sequence of any of (A) to (C)； an amino acid sequence which is the same as the amino acid sequence represented by the reverse sequence of (A) except that one or several basic amino acids are substituted, deleted, inserted and/or added； or an amino acid sequence which is the same as the amino acid sequence represented by the reverse sequence of (A) except that 1 to 5 amino acids are substituted, deleted, inserted and/or added； which peptide has cell membrane permeability.이하의 (A)～(D) 중 어느 하나의 세포막 투과성 펩티드는 친수성 생리활성물질에 세포막 투과성, 및 점막 흡수성을 부여한다. (A) 서열번호 1로 표시되는 아미노산 서열로 이루어진 펩티드. (B) 서열번호 1로 표시되는 아미노산 서열에 있어서 1개 또는 수개의 염기성 아미노산이 치환, 결실, 삽입 또는 부가된 아미노산 서열로 이루어지고, 또한 세포막 투과성을 갖는 펩티드. (C) 서열번호 1로 표시되는 아미노산 서열에 있어서 1～5개의 아미노산이 치환, 결실, 삽입 또는 부가된 아미노산 서열로 이루어지고, 또한 세포막 투과성을 갖는 펩티드. (D) (A)～(C) 중 어느 하나의 역서열로 표시되는 아미노산 서열 등의 아미노산 서열로 이루어지고, 또한 세포막 투과성을 갖는 펩티드.
