The purpose of this study was to investigate the phytochemical analysis of D. pentaphyllum and its cytotoxic activity on human cervical cancer (HeLa) cells with possible mechanisms. Total phenolic contents (TPC) and phytochemical analysis of the extract were evaluated using spectrophotometric method and RP-HPLC, respectively. The cytotoxic effect of the extract was evaluated using the MTT assay. The mechanism of the cytotoxic effect of the extract was also evaluated in terms of apoptosis, cell cycle, and mitochondrial membrane potential (MMP) using the fluorometric methods. The TPC of the extract was calculated as 68.9 +/- 2.3 mg gallic acid equivalent per g sample and quercetin was determined as the major phenolic in the extract. The extract showed a selective cytotoxic effect (6.5-fold) on HeLa cells compared to normal fibroblast cells. The cytotoxic effect of the extract was found to be due to the arresting of the cell cycle in the S phase and increasing apoptosis through decreased MMP. Further studies are needed for the comprehensive effects of the extract on cell signaling.