Nanoparticles are used in various applications due to unique mechanical and physicochemical properties such as their increased surface area to volume ratio and quantum effects. This study was designed to investigate the cytotoxic effects of zinc oxide nanopaticles on hematological and biochemical parameters BALB/c mice. Materials and Methods: In this experimental study, 28 adult male mice BALB/c, were divided into four groups (one control group and three experimental groups). The mice in the

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... erimental groups orally received Zinc Oxide nanoparticles with doses of 50, 100 and 300 mg/kg for 14 days. The control group received distillated water only. On 15th day, some hematological and biochemical parameters were studied on the blood samples collected. Results: Results showed that Zinc Oxide nanoparticles cause changes in blood cells. In high concentration, nanoparticles increased some of factors such as white blood cells, hemoglubin, MCV and neutrophil and besides decreased amount of RBCs, pLTs, hematocrit, lymphocytes, glucose and kratenin significantly (p<0.05). Conclusion: The findings showed that zinc oxide nanoparticles cause harmful effects due to the considerable variations in hematological and serum parameters in mice in a dose-dependent way.