Triptolide is used in traditional Chinese medicine. It has the advantages of a unique mechanism of action, a wide antitumor spectrum, multiple targets, multi-channel effects and low toxicity. The current study was conducted to evaluate whether the potential anticancer effects of triptolide reduces proliferation and enhances apoptosis of human non-small cell lung cancer (NSCLC) cells, and to assess the underlying anticancer mechanisms. In PC-9 cells, treatment with triptolide reduced cell proliferation and increased cell apoptosis and caspase-3 and 9 activity. Triptolide treatment reduced miR-21 expression and enhanced phosphatase and tensin homolog (PTEN) protein expression levels in the PC-9 cells. Furthermore, the upregulation of miR-21 expression levels suppressed the effect of triptolide on cell viability and PTEN protein expression levels in PC-9 cells. To the best of our knowledge, the present study is the first to demonstrate that triptolide reduced the proliferation and enhanced the apoptosis of human NSCLC cells through PTEN by targeting miR-21.