Abstract: The interaction between photoradiation-hematoporphrin derivative (HPD) and liposome was studied with fatty acid spin label and ESR spectrum by white light, infrared laser and ultraviolet laser. It was found that photoradiationHPD increased the permeability of the liposome largely. The effect of infrared and ultraviolet laser was found to be stronger than that of white light and the effect of ultraviolet was stronger than that of infrared laser. Photoradiation-HPD was shown to decrease the intensity of the ESR signal of the fatty acid spin label incorporated in this system. Photoradiation-HPD was also found to decrease the order of the phospholipid molecule in the liposome slightly.