Copper oxide nanoparticles (CuO NPs) are commonly used in many industrial and biomedical applications. Excessive usage of these products may lead to their discharge into aquatic ecosystems causing harmful ecotoxicological hazards. The present study was performed to assess the impact of CuO NPs on mortality, bioaccumulation, oxidative stress, histopathology of the hepatopancreas and DNA damage of the red swamp crayfish Procambarus clarkii. The assessment of such effectsof Cu NPs may be useful for understanding the mechanism of their toxicity and evaluation of the possibility of using nanoparticles-induced alterations in the investigated organism as pollution biomarkers. For these purposes, adult crayfishes were exposed to 25, 125 and 250 mg/l of CuO NPs for 28 days. Percentages of mortalities were 0%, 6.7% and 36.7%, for application of these concentrations respectively. Bioaccumulation analysis revealed that the highest accumulation levels of copper were observed in gills followed by hepatopancreas while the lowest was detected in muscles. Biochemical analysis showed that exposure of P. clarkii to the above concentrations of CuO NPs caused significant increase in the activities of lipid peroxidation (LPO), Catalase (CAT), Glutathione-S-transferase (GST) and Metallothioneins (MTs) in hepatopancreas. On the other hand, levels of glutathione (GSH), total lipids (TL) and total proteins (TP) were significantly decreased. Light microscopical examinations of the hepatopancreas exposed to CuO NPs revealed lumen dilatation, increased yellowish brown granules, vacuolation, nuclear pyknosis and cellular lysis in the hepatopancreatic epithelial cells. At the electron microscopiclevel, vacuolated cytoplasm with densely stained secretory granules, fragmented microvilli of absorptive cells, ruptured RER, and deformed mitochondria were noticed. Comet assay analysis showed that high concentrations of these nanoparticles caused nuclear DNA damage. In conclusion, CuO NPs induced many histopathological and biochemical alterations in P. clarkia which are clear enough to be used as biomarkers for CuO NPs exposure.