We incorporated an amphiphilic azobenzene derivative, 4-actyl-4’-(5-carboxypentamethyleneoxy) azobenzene (8A5),into the liposome membrane of L-alpha-dimyristoylphosphatidylcholine (DMPC). Photoisomerization of 8A5 and changes in K+ ion permeability, P cm s(-1), of the membrane under irradiation with ultraviolet light were examined. The temperature of the liposome dispersion was controlled in the range T=283-303 K. Trans-to-cis isomerization of 8A5 induces the increase of ion permeability in the whole temperature range. A specific permeability enhancement is observed around T=290-293 K, where the ratio P(cis)/P(trans) amounts to 200-300. It is suggested that the permeability enhancement around the phase transition temperature is caused by the increase of the phase separation boundaries as well as by the expansion of pores due to trans-to-cis isomerization.