Provided are peptides imparting cell permeability to a lipid membrane structure and/or enhancing the cell permeability of a lipid membrane structure, and a lipid membrane structure which comprises, as a constituent lipid, a lipid bound to such a peptide and has cell permeability or shows enhanced cell permeability. The amino acid sequences of the peptides imparting cell permeability to a lipid membrane structure and/or enhancing the cell permeability of a lipid membrane structure are represented by: LX 1 X 2 X 1 X 1 X 1 L, LLX 2 X 1 X 1 X 1 L and LX 1 X 2 X 1 X 1 L (wherein L represents a leucine residue X 1 represents a polar amino acid residue and X 2 represents a polar, non-charged and branched chain amino acid residue).
