Recently, there has been growing attention and effort to search for new microbicidal drugs which present different mode of action from those already existing, as an alternative to the global threat of fungal and bacterial multi drug resistance (MDR). Here we propose biological synthesis of SnO₂ nanoparticles using mammalian cells as an economic and ecofriendly platform. This presents a novel biogenic method for SnO₂ synthesis using metal binding peptides extracted from MCF-7 human cancer cells, which induces the biomineralization of SnO₂ nanoparticles. A series of electron donor functional groups and metal binding sites in these peptides reacts with Sn2+ ions and directs the growth of SnO₂ nanoparticles without addition of toxic redox and capping agents in the reaction system. Since peptides present reactive sites in aqueous solution at room temperature, a facile reaction environment can be easily achieved. Furthermore, by tuning the reactants' concentration and pH, the size, shape and 3D-structures of SnO₂ nanoparticles can be controlled. Peptides also ensure biocompatibility, and SnO₂ nanoparticles provide antibacterial properties, which broadens their applications in biomedical fields.