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Objectives As a parenchymal cell, the photoreceptor is more susceptible to alterations in outer micro-environmental conditions than other cells. In the present study, we aimed to investigate inhibitory effects of zinc oxide (ZnO) nanoparticles on expression of manganese superoxide dismutase (MnSOD) in murine photoreceptor-derived cells. Materials and methods We investigated effects of ZnO nanoparticles on murine photoreceptor cell viability and on expression and activity of MnSOD using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, immunofluorescence analysis, flow cytometry, quantitative real-time PCR and enzyme-linked immunosorbent assay (ELISA). Results ZnO nanoparticles were found to have higher cytotoxic effects in concentration- and time-dependent manners, to elevate intracellular levels of hydrogen peroxide and hydroxyl radicals, and thus to induce overproduction of reactive oxygen species (ROS) and collapse of mitochondrial membrane potential, leading to cell damage. Moreover, ZnO nanoparticles also significantly reduced expression of MnSOD at both the mRNA and protein levels, reduced its activity, and further aggravated oxidative stress-mediated cell damage. Conclusion Overall, ZnO nanoparticle-induced cytotoxicity was associated with elevated levels of oxidative stress due to overproduction of ROS and reduced expression and activity of MnSOD.