Little information is available on the bioavailability and genotoxicity of ENPs in grass carp Ctenopharyngodon idella. Seven days old grass carp larvae have been exposed to 1, 5, 10, 50, 100 mgl-1 copper oxide nanoparticles for a week. There was no difference in mortality between treated groups and control. Whole body copper concentrations increased significantly in all exposure groups except in 10 mgl-1 group. The genotoxicity of copper oxide nanoparticles was evaluated using DNA laddering technique. Copper oxide nanoparticles were found to be genotoxic at a low concentrations followed by a decrease in extent of DNA damage at higher concentrations.