A novel triterpenoid, named 3β-trans-cinnamoyloxy-2α-hydroxy-urs-12-en-28-oic acid (CHUA), was one of the main components of apple peels and showed potent in vitro antitumor activity against human tumor cells. In vivo antitumor experiments showed that CHUA could significantly inhibit the growth of mammary tumor in a nude mouse xenograft model at a dose of 50 mg/kg/day without body weight loss and mortality. In vitro, CHUA could induce apoptosis in MDA-MB-231 cells through the detection of DNA fragments and LDH activity. Simultaneously, mitochondrial transmembrane potential was markedly reduced and the release of cytochrome c was increased after CHUA treatment. It also up-regulated the expression ratio of mitochondrial Bax/Bcl-2 regulated by SIRT1 and p53. Interestingly, z-VAD-fmk and z-DEVD-fmk augmented cell death after CHUA treatment. Other protease(s) different from caspase-3 might be responsible for the degradation of PARP. These results suggested that the pro-apoptotic activity of CHUA may be adjusted by mitochondrial and caspase-independent pathways.