The purpose of the present invention is to provide an electrostatically bonded vesicle which bears disulfide bonds or thiol groups. The present invention relates to a vesicle having a membrane which is formed from both a first polymer of (a) or (b) and a second polymer of (c) or (d) (with the proviso that a combination of (b) and (d) is excepted) and in which the cationic segment and anionic segment of the polymers are partially crosslinked. First polymer: (a) a block copolymer (I) having both an electrically non-charged hydrophilic segment and a cationic segment, (b) an amino acid polymer (I) having a cationic segment. Second polymer: (c) a block copolymer (II) having both an electrically non-charged hydrophilic segment and an anionic segment, (d) an amino acid polymer (II) having an anionic segment.
