Biological synthesis of nanoparticles is a growing research trend because it has numerous applications in pharmaceutics and biomedicine. The aim of this study was to obtain silver nanoparticles (AgNPs) from Bacillus sp. KFU36, a marine strain, and to assess its anticancer activity. The supernatant of Bacillus sp. KFU36 was supplemented with silver nitrate and the nanoparticles obtained were characterized spectrophotometrically and microscopically. A band of surface plasmon resonance was appeared at 430 nm, as revealed by UV–vis spectrophotometry. X-ray diffraction spectrum and Energy Dispersive Spectroscopy confirmed the crystalline and metallic structure of the AgNPs, respectively. Scanning electron microscopy revealed that the shape of the synthesized AgNPs were spherical and the size extended between 5 and 15 nm. The AgNPs were investigated for their potential anticancer effects on the cell viability, migration and apoptosis using MTT and wound-healing assays, and flow cytometry, respectively. The cytotoxic effects of these nanoparticles were evidenced by the decreasing the cell viability (as 15% at 50 μg/ml), cell density, adhesion capacity and losing the normal shape and size, and inducing the apoptosis on MCF-7 by 61% at 50 μg/ml. These findings confirm that the synthesized AgNPs exhibited superior anticancer activities and therefore could be exploited as a promising, cost-effective, and environmentally benign strategy in treating this disease in future.