OBJECTIVE To investigate apoptosis induced by photodynamic therapy with benzoporphyrin derivative monoacid ring A (BPD-MA) and explore its potential mechanism in human bladder cancer cells.METHODS Photosensitization of BPD-MA was activated with a red light Laser (632.8nm) delivered at 10 mW/cm2 to give a total dose of 2.4 J/cm2.Cellular apoptosis was measured with flow cytometry analysis and an insitu terminal deoxyuridine nick end-labeling (TUNEL) assay. Changes in mitochondrial membrane potential (△ψm) were monitored by a flow cytometric method with Rhodamine 123 staining and the expression of bcl2 in BIU-87 cells was detected with immunocytochemical staining.RESULTS At 8 h following photodynamic treatment, the degree of apoptosis was significantly increased when analyzed with flow cytometry and TUNEL assay. Treatment of the BIU-87 cells by PDT with BPD-MA resulted in the collapse of the △m and a decrease of bcl-2 expression.CONCLUSION BPD-MA-mediated PDT can effectively induce apoptosis in BIU-87 cells. The mechanism probably is through a mitochondrial-initiated pathway.