Saponin is an important class of natural products that can be presented in many plants, it has a diverse range of properties, which include pharmacological and medicinal properties, antimicrobial, insecticidal, and anticancer activities. The aim of this study was to extract the saponin from different Egyptian legumes sources and evaluate the antitumor activity of partially purified saponin extracted from soybean in mouse colon cancer cells in vitro and compare its activity with cisplatin as reference chemotherapeutic drug. In this study saponin extracted from soybean and partially purified using silica gel column chromatography and then characterized by using IR and HPLC techniques. Antitumor activity of partially purified saponin was evaluated by using MTT assay, caspase-9 activity and apoptotic effect by flow cytometric analysis. Our results showed that the high saponin was present in soybean with concentration 94.8 mg/g dry weight. The partially purified soybean saponin inhibited the proliferation of colon cancer cell line in a dose-dependent manner with IC50 43.4 μg/ml after 48 hrs treatment. The proliferation inhibitory effect of soybean saponin was associated with its apoptosis-inducing effect by activation of caspase-9 and increasing the percent of apoptotic cells to 91.02% when compared with negative control after analysis by flow cytometry. In conclusion, soybean saponin had antitumor activity against mouse colon cancer cell line and its mechanism was mediated through apoptotic effect.