The present invention provides an amphiphilic molecule having a plurality of zwitterionic functional groups in its hydrophilic moiety and a molecular assembly comprising the amphiphilic molecule as a constituent lipid. The molecular assembly of the present invention forms a stable vesicular structure under a physiological pH environment to carry a substance of interest in the vesicular structure, and can release the substance of interest to the outside of the vesicular structure when it is deformed under an acidic pH environment. The molecular assembly of the present invention can be used as a carrier for a drug, a probe, a nucleic acid, a protein or the like.
