Copper oxide nanoparticles (CuO NPs) are used in antimicrobial preparations, heat transfer ﬂuids, semi-conductors or intrauterine contraceptive devices. Nanoparticles with unique magnetic, luminescent, and catalytic properties are being engineered for numerous biomedical applications, including imaging, diagnostics and therapy. However, potentially harmful interactions can occur between nanoparticles and living systems, including humans. The present study was aimed to assess the cytotoxicity of CuO NPs in human alveolar epithelial cell line (A549). A reduction in cell viability as a function of NP concentration for 24h was observed. CuO NPs were also found to induce oxidative stress in cells indicated by generation of H2O2. Our data demonstrates that CuO NPs even at low concentrations lead to cell membrane damage in human epidermal cells which may be mediated through lipid peroxidation and oxidative stress, however, induced little effect to Mitochondria. Hence, caution should be taken in their widely use as well as while handling.