Thermograms of methylene blue(MB) in L-α- lecithin vesicle and incorporated purple membrane vesicle(InPM) systems have been studied by photochemical reaction differential scanning calorimetry at 25∼55℃. Phase transition temperatures of lecithin vesicle, purple membrane(PM), and InPM were found to be independent of illumination of light(436nm) at 39∼40℃, but endothermic phase transition was found in InPM vesicle. In MB-InPM system, endothermic phase transition was found on unillumination of light at 40∼42℃, but exothermic phase transition was found on steady illumination of light at 48∼52. It was estimated that the light energy absorbed from MB on vesicular surface was transferred to PM, and the transferred energy was redistributed to hydrophobic site of membrane. Therefore, the exothermic phase transition was measured at high temperature because of the increased hydrophobicity of acyl chain.