The present study was conducted to examine cytotoxic, apoptotic, and necrotic effects of silver nanoparticles (AgNPs) on MCF-7 cells. Colloidal AgNPs were fabricated in an alkaline pH environment via reduction of silver nitrate with hydroxylamine hydrochloride. The size of AgNPs was measured by atomic force microscopy (AFM), transmission electron microscopy (TEM), and dynamic light scattering. Zeta potential of AgNPs was determined by laser Doppler microelectrophoresis. After exposing MCF-7 cells to AgNPs for 24 h, cytotoxicity was measured by WST-1 assay. Apoptosis and necrosis in MCF-7 cells were detected by Annexin-V-FLUOS immunostaining and double staining of Hoechst dye with propidium iodide. In AFM and TEM analyses, the sizes of AgNPs varied from 16 nm to 20 nm. AgNPs were 80 nm in hydrodynamic diameter with a zeta potential of –38.2 mV. The WST-1 assay resulted in an IC50 value of 40 µg/mL. AgNPs caused apoptotic and necrotic effects in a dose-dependent manner. The apoptotic effect of AgNPs was marked up to a concentration of 80 µg/mL AgNPs. At higher concentrations, the apoptotic effect decreased while the necrotic effect became prominent. The results indicate that AgNPs with a zeta potential of –38.2 mV and hydrodynamic diameter of 80 nm can be used in vitro at concentrations of up to 40 µg/mL. ; The present study was conducted to examine cytotoxic, apoptotic, and necrotic effects of silver nanoparticles (AgNPs) on MCF-7 cells. Colloidal AgNPs were fabricated in an alkaline pH environment via reduction of silver nitrate with hydroxylamine hydrochloride. The size of AgNPs was measured by atomic force microscopy (AFM), transmission electron microscopy (TEM), and dynamic light scattering. Zeta potential of AgNPs was determined by laser Doppler microelectrophoresis. After exposing MCF-7 cells to AgNPs for 24 h, cytotoxicity was measured by WST-1 assay. Apoptosis and necrosis in MCF-7 cells were detected by Annexin-V-FLUOS immunostaining and double staining of Hoechst dye with propidium iodide. In AFM and TEM analyses, the sizes of AgNPs varied from 16 nm to 20 nm. AgNPs were 80 nm in hydrodynamic diameter with a zeta potential of –38.2 mV. The WST-1 assay resulted in an IC50 value of 40 µg/mL. AgNPs caused apoptotic and necrotic effects in a dose-dependent manner. The apoptotic effect of AgNPs was marked up to a concentration of 80 µg/mL AgNPs. At higher concentrations, the apoptotic effect decreased while the necrotic effect became prominent. The results indicate that AgNPs with a zeta potential of –38.2 mV and hydrodynamic diameter of 80 nm can be used in vitro at concentrations of up to 40 µg/mL.