Abstract: This is a report of clinical observation of photodynamic therapy in 7 cases of human brain malignant tumors and a preliminary exploration of animal experimentation.It is concluded that HPD has certain significant usefulness in diagnosis of brain tumor.But the long-term treatment effect of this modality remains to be further evaluated.The results of animal experimentation show that the normal brain tissues contain extremely small amount of HPD due to the existance of blood-brain barrier,so fluorescence does not appear in them.Nevertheless,HPD can still damage brain tissues under lasser.Therefore,protection of surrounding tissues is very important when laser is used.The amount of HPD reaches the highest level in brain tumor 4 hours after administration.The HPD ratio in the brain tumor/in the normal brain tissue is 53:1.The use of laser treatment shortly after the administration of HPD may be considered optimal as the time of the former application is concerned.