Ent-11α-hydroxy-15-oxo-kaur-16-en-19-oic-acid (5F) is a chemical compound isolated from Pteris semipinnata L (PsL), a Chinese traditional herb. 5F has been known to exert antitumor activity in several kinds of human malignant cancer cells by leading cancer cell to apoptosis. 5F translocated Bax into the mitochondria, down-regulated Bcl-2, activated caspase-9 and caspase-3, released cytochrome c into the cytosol and translocated AIF from the mitochondria to the nucleus. The presentation of a wild-type p53 in the cancer cells facilitated cancer cells sensitive to the 5F treatment. 5F induces apoptosis of cancer cells by inhibiting NF-κB activation/induction, which leading to the decrease of Bcl-2 but the increase of Bax and Bak. MAPK kinases and Akt are also involved in process of 5F inducing cancer cell apoptosis. In lung cancer, 5F activated ERK1/2 and the inhibition of ERK1/2 suppressed 5F-mediated changes in apoptotic molecules. 5F activated Akt and suggested that Akt activation was anti-apoptotic rather than pro-apoptotic. However, in anaplastic thyroid carcinoma, JNK activation was related to cell death induced by 5F. ERK and p38 were also activated but as survival signals in response to 5F treatment to counteract the induction of cell death. Collectively, 5F is effective against several malignant cancers both in vivo and in vitro with minimal side effects. It induces apoptosis through the mitochondrialmediated pathway, in which regulation of Bcl-2 family proteins expression, the activation of MAPK and inactivation of NF-κB are critical. The good ability of 5F to inhibit cancer cells makes it in line with the successful development of other anti-tumor agents.