Objectives. In this study, we investigate that methanol extract of Euphorbiae lathyridis Semen contributes to growth inhibitory effect on the HT-29 human colon cancer cells. Methods. Euphorbiae lathyridis Semen (ELS) was extracted with 80% methanol. HT-29 cells were treated with different concentrations of ELS extract for 24-72 hrs. Growth inhibitory effect was determined by MTT assay. Cell apoptosis was determined by surveying caspases cascades activation using Western blot. Cell cycle arrest was analyzed by flow cytometry with PI staining. Results. Exposure to ELS extract showed in inhibitory effects on HT-29 cell growth as a dose-dependent manner. Cell growth inhibition by ELS extract was related with induction of cell apoptosis with DNA fragmentation through the activation of caspases-3, caspase-9 and PARP cleavage. Conclusion. ELS extract significantly inhibited cell growth and induced cell apoptosis in HT-29 human colon cancer cells, therefore, These results suggest that ELS extract can be used as chemoprevention agent of colon cancers.