In this study, we investigated the effect of amine-and hydroxyl-terminated Generation 2 and 3 (G2 and G3) poly (amidoamine)(PAMAM) dendrimers on the viability and induction of apoptosis in human MCF-7 and MDAMB-231 breast cancer cells. It was shown that amino-terminated PAMAM dendrimers were cytotoxic, with IC50 value after 24 hr of incubation in MCF-7 and MDA-MB-231 breast cancer cells 153±3 μM and 140±2 μM for G2 PAMAM and 120±3 μM and 99±2 μM for G3 PAMAM, respectively. Experiments made with annexin V-fluorescein isothiocyanate (V-FITC) and detection of apoptosis by a fluorescent microscopy assay revealed that G2 and G3 PAMAM-NH2 dendrimers inhibited the proliferation of MCF-7 and MDA-MB-231 malignant cells by increasing the number of apoptotic and necrotic cells. The cytotoxic and apoptotic effect of G2 and G3 PAMAMOH dendrimers was significantly weaker.