Triptolide (TP), the primary active component purified from the traditional Chinese herbal medicine Tripterygium wilfordii Hook. F (TWHF), has been shown to possess antitumor activity in several types of solid tumors. In the present study, we investigated the antitumor effect of TP in human endometrial cancer cells (HEC-1B) and elucidated its possible underlying mechanisms. HEC-1B cells were treated with various doses of TP (10, 20, 40, 80, 160 and 320 nM), and the cell viability was assessed by Cell Counting Kit-8 (CCK-8) and flow cytometric analysis. Results indicated that TP inhibited the proliferation of HEC-1B cells in a dose- and time‑dependent manner. To further investigate its mechanisms, the levels of apoptosis and the changes in caspase-3/9 expression in HEC-1B cells by pretreatment with z-VAD-fmk, a pan-caspase inhibitor, were detected by CCK-8 and western blotting. The cytotoxic effects of TP were significantly inhibited by z-VAD‑fmk. At the molecular level, TP did not effectively activate the p53 signaling pathway, but upregulated caspase-3/9 and downregulated bcl-2 without changing the bax level. Our studies revealed that TP has an effect on the apoptotic ability of endometrial cancer cells via a p53-independent mitochondrial pathway, presenting a novel strategy to evade drug resistance in tumorigenesis. The ability of TP to be a potential chemotherapeutic agent for endometrial cancer should be considered.