Nanoparticles are being designed with chemically modifiable surfaces to attach a variety of molecules to improve biosensing, imaging techniques, delivery vehicles, and other useful biological tools. Keeping this in view, the present research work is focused on investigation of cytotoxicity of metal oxide nanoparticles. Different metal oxide nanoparticles (e.g titanium dioxide, zinc oxide, iron oxide, aluminum oxide etc) of different sizes and different concentrations were used to investigate the cellular response. Electron microscopy and colorimetric assays were used to characterize the various process steps. Zirconium oxide nanoparticles were used in suspension form stabilized with stabilizer and the others were used as their aqueous suspension. Results clearly reflect that as the concentration increases, cytotoxicity also increases. As aggregation occurs, cytotoxicity decreases. In suspension with stabilizer, cytotoxicity is more as compared to aqueous suspensions.