The cytotoxic activitiy of silver nanoparticles bio-functionalized by Nelumbo nucifera leaf extracts were examined in the current work. The nanoparticle (AgNPs) was characterized by scanning electron microscopy, UV–visible spectroscopy, and a particle size analyzer. Cytotoxic activity of silver nanoparticles against T47D and 4T1 cells using the MTT method using concentrations of 100 µg/mL, 50 µg/mL, and 25 µg/mL. For comparison, doxorubicin was used at the same dose. The size of the spherical nanoparticle was 66.4±0.93 nm and the polydispersity index was 0.23±0.05. Silver nanoparticles have anti-cancer properties against T47D and 4T1 cell lines based on inhibitory concentration. The inhibitory concentration (IC50) of AgNPs on T47D and 4T1 cells were obtained at 12.10±0.08 𝜇g/mL and 98.77±1.27 𝜇g/mL, respectively. Meanwhile, the IC50 values of doxorubicin in T47D and 4T1 cells were 4.45±0.03 𝜇g/mL and 36.77±1.15 𝜇g/mL, respectively. Overall, the results revealed that the green-synthetized silver nanoparticle had cytotoxic effects on breast cancer cells in comparison to doxorubicin.