We report the effect of laser wavelengths and HpD on diffuse reflectance of tumor surface in mice.Three kinds of lasers (Ar +,Nd:YAG and He Ne lasers) of six different wavelengths and hemetoporphyrin derivative (HpD) as photosensitizer were used in the experiment.Tumor bearing mice were divided into two groups.The mice of one group were given an i.p.injection of HpD 10mg/kg.24 hours later,the laser diffuse reflectance of tumor surface of the mice of two groups were measured by a single integrating sphere system with laser in six wavelengths (476.5nm,488.0nm,496.5nm,514.5nm,632.8nm,and 1060nm).The results of measurement showed that significant difference of diffuse reflectance on tumor surface between the visible laser light and infrared laser light were observed.There was no significant difference in diffuse reflectance on tumor surface with and without i.p.injection of HpD.So it is unnecessary to consider the effect of HpD when calculating the actual laser dose irradiated into the tumor.The diffuse reflectance of tumor surface reaches its maximum at 1060nm wavelength,as twice as at 514.5nm wavelength.It is hence concluded that diffuse reflectance should be taken into consideration when calculating the actual laser density for irradiation on tumors.