Abstract: Photodynamic therapy（PDT）was used in the present study to induce cell apoptosis and cell necrosis. The kind of cell death mode was determinated by the PDT dose. Low doses could induce cell apoptosis, while the high doses could induce cell necrosis. Whether a cell died by necrosis or apoptosis highly likely depended on the speed of intracellular ROS generation after PDT treatment. This study will aid in the understanding of the mechanisms related to PDT-induced cell death.