Background: Our earlier study on the antiproliferative (APF) activity of leaf extracts of ten Apocynaceae species showed that leaves of Vallaris glabra possessed strong and broad-spectrum properties. Materials and Methods: In this study, sequential extracts of leaves, flowers and stems, and fractions and isolated compounds from dichloromethane (DCM) leaf extract of V. glabra were assessed for APF activity using the sulphorhodamine B (SRB) assay. Apoptotic effect of MDA-MB-231 cancer cells treated with DCM leaf extract of V. glabra was studied using Hoechst 33342 dye and caspase colorimetry. Results: Both DCM extracts of leaves and flowers possessed broad-spectrum APF activity against HT-29, MCF-7, MDA-MB-231 and SKOV-3 cancer cells. From DCM leaf extract, stearic acid (SA) and ursolic acid (UA) were isolated by column chromatography, and identified by NMR and MS analyses. APF activity of SA from DCM leaf extract displayed weak inhibitory activity and scientific literature showed UA has anticancer properties against those cancer cells used in this study. MDA-MB-231 cancer cells treated with DCM leaf extract and stained with Hoechst 33342 dye provided evidence that the extract had an apoptotic effect on the cells. Caspase colorimetry showed that the apoptotic effect involved activation of caspase-8, -9 and -3, but not caspase-6. Conclusion: The potential of V. glabra as a candidate species for anticancer drugs warrants further investigation.