Abstract. Kiseueur (Antidesma tetrandrum blume) is an Indonesian native plant that is potential as an anticancer drug. This study aimed to determine the cytotoxic activities and apoptosis inducing mechanism of the extract and fraction of Kiseueur leaves and bark in breast cancer cell lines (MCF-7). The cytotoxic activity was carried out using the MTS assay. The expression of caspase 3 and caspase 9 pro-apoptotic proteins was observed by Western blot analysis. The results showed that the extract and fraction of Kiseueur leaves and bark had varied cytotoxic activities in breast cancer cell lines (MCF-7). Kiseueur bark extract had the highest cytotoxic activity against MCF-7 cells with IC50 81.65 μg / mL. Kiseueur bark extract induced apoptotic mechanism through modulation of caspase 9 and caspase 3 protein expression.