Gallbladder carcinoma is the most common malignancy of the biliary tract, with a very low 5-year survival rate and extremely poor prognosis. Thus, new effective treatments and drugs are urgently needed for the treatment of this malignancy. In this study, for the first time we investigated the effects of triptolide on gallbladder cancer cells and identified the mechanisms underlying its potential anticancer effects. The MTT assay showed that triptolide decreased cell viability in a dose- and time-dependent manner. The results of the colony formation assay indicated that triptolide strongly suppressed colony formation ability in GBC-SD and SGC-996 cells. Flow cytometric analysis revealed that triptolide induced S phase arrest in gallbladder cancer cells. In addition, triptolide induced apoptosis, as shown by the results of annexin V/propidium iodide double-staining and Hoechst 33342 staining. Furthermore, triptolide decreased mitochondrial membrane potential (ΔΦm) in a dose-dependent manner. Finally, western blot analysis of triptolide-treated cells revealed the activation of caspase-3, caspase-9, PARP, and Bcl-2; this result demonstrated that triptolide induced apoptosis in gallbladder cancer cells by regulating apoptosis-related protein expression, and suggests that triptolide may be a promising drug to treat gallbladder carcinoma. © 2014 by the authors; licensee MDPI, Basel, Switzerland.