In a previous study, ethyl acetate extract of Coprinus comatus was found to reduce viability of human ovarian cancer cells. The objective of the current research was to clarify the mechanism of action of this extract. Ovarian cancer cells (ES-2) were subjected to ethyl acetate extract of C. comatus for different concentrations or exposure times. Cell cycle analysis and annexin V staining were performed using an automated flow cytometer. DNA fragmentation was detected using the TUNEL assay. Western blot analysis was performed for the assessment of activation of caspases -3, -8, and -9. Results revealed that treatment of ES-2 cells with ethyl acetate extract of C. comatus (100 μg/ml medium), for 48 h or for 72 h resulted in an increased number of cells at the sub-G1 phase of the cell cycle. These treatments also resulted in an increased number of apoptotic cells (positively stained by annexin and positively labeled by TUNEL), in comparison to the control. Reduced levels of procaspases -3, -8, and-9 were also detected in treated cells. In conclusion, ethyl acetate extract of C. comatus induces apoptosis in ovarian cancer cells (ES-2), via both extrinsic and intrinsic pathways. Meanwhile, more investigations are needed to demonstrate weather the apoptotic effect on ovarian cancer cells is accomplished by one active compound, or combined activities of different compounds that exist in the extract.