Abstract: In order to study the mechanism of photodynamic therapy on malignant tumors,photosensitization of BPD-MA is activated by laser with red light(632.8nm) delivered at 10mW/cm2to give a total dose of 2.4J/cm2.Apoptosis of human bladder cancer BIU-87 cells is determined with flow cytometry with PI staining and terminal deoxyuridine nick end labeling(TUNEL) assays.Results show that photodynamic therapy with BPD-MA significantly increases the rate of apoptosis in BIU-87 cells.A lot of the positive cells in which their nucleus is brown-yellow fine particle shape or overflowing-dispersed are observed after treatment of cells with photodynamic therapy with BPD-MA.However,laser irradiation alone,BPD-MA alone and sham radiation without BPD-MA can not affect apoptosis of human bladder cancer BIU-87 cells.A conclusion can be made that treatment of cells with photodynamic therapy obviously induces human bladder cancer BIU-87 cells to apoptosis,which may be one of the important mechanism of photodynamic therapy on malignant tumors.