Photodynamic therapy (PDT) involves the use of photochemical reactions mediated through the interaction of photosensitizing agent for the treatment of malignant tumor. The present study was carried out to evaluate the photosensitizing potential of embelin isolated from Embelia ribes. For PDT study, cells were grouped into four groups. Two types of control were used, one with Ehrlich's ascites carcinoma (EAC) cells alone (group 1) and one which received the illumination alone (group 2). Group 3 contains cells treated with different concentrations of embelin for 1 h at 37 A degrees C. Another set of cells (group 4) after treatment with different concentrations of embelin was illuminated in ice for 4 min with a 1000-W halogen lamp. To study the mechanism of cell death, the following parameters such as reactive oxygen species (ROS), caspase-3, lactate dehydrogenase (LDH), and thiobarbituric acid reactive substances (TBARS) were analyzed both in the absence and presence of light after the treatment of embelin. PDT study clearly indicated that embelin alone recorded no cytotoxicity, but for light treatment alone with the different concentrations of embelin, there was a significant induction of cytotoxicity in a concentration-dependent manner. Level of ROS and LDH increased in cells treated with embelin. Moreover, caspase-3 also increased which clearly indicated that cell death is through caspase-dependent apoptosis. This is the first report on PDT, a novel modality, using embelin for cancer therapy in vitro. The novelty of the study depends on the fact that cytotoxicity was produced by the synergistic effect of the embelin and light.