The purpose of this study was biogenic synthesis of silver nanoparticles using aqueous leaf extract of Cissus woodrowii (CW-AgNPs) and exploration of their role in inhibition cell proliferation of breast cancer cells. Inhibitory effect of biogenic CW-AgNPs on cell proliferation of MCF-7 cells was determined by MTT assay. Apoptotic cell death was demonstrated by caspase-3 assay, DNA fragmentation assay, Annexin-V-FITC/PI staining assay and cell cycle arrest assay by flow cytometry. Expression of apoptosisrelated genes including caspase-3, p53 and Bcl2 was studied by western blot analysis and semi-quantitative RT-PCR. Results of UV-Vis spectrum of colloidal solution of CW-AgNPs showed surface plasmon resonance peak at 430 nm. TEM and XRD results confirmed spherical shaped, 20-30 nm sized nanoparticles. Cell proliferation results showed inhibitory effects of CW-AgNPs on MCF-7 with IC 50 (24 h) 8.48 µg/ mL and (48 h) 7.11 µg/mL. The CW-AgNPs altered cell morphology of MCF-7 cells and induced apoptosis significantly which was evidenced through caspase-3 activation and nuclear DNA fragmentation. The results were supported by the observation of Annexin-V-FITC/PI staining and cell cycle arrest assays. The up-regulated expression of both p53 and caspase-3 genes and down-regulation of Bcl2 at both protein and mRNA level supported their role in induction of apoptosis in MCF-7 cells in response to CW-AgNPs. The findings obtained in current study supported the role of biogenic CW-AgNPs in inhibition of cell proliferation in breast cancer cells through induction of apoptosis.