The present study deals with acute toxicity and hematological, histopathological and genotoxical effects of permethrin, a synthetic pyrethroid, on Pseudorasbora parva. Acute toxicity of 96-hrs LC50 value was found to be 88.25 (84.60-92.63) mu gl(-1). Sublethal dose was taken as 8.82 mu gl(-1) (the 1/10 of the LC50 value) in bioexperiments. Micronucleus changes in blood erythrocyte and hemotocyte level in P. parva exposed to sublethal concentration were investigated. Difference between nucleolus abnormalities in the experimental and control group was found to be statistically significant (t-test). Micronucleus frequency was found to be 8.26. The hematocrit level in control and experimental groups were found to be 24.43% and 14.673%. No pathological symptoms were observed in the muscle of P. parva exposed to sublethal dose for 96 hrs. Pathological symptoms observed after 96 hrs from permethrin administration in other organs were: Fusion, Telangiectasis, epithelial lifting and hyperemia in gills; hydropic degeneration, lipid degeneration and passive hyperemia in liver and enlargement of cavum glomeruli and Bowman space in kidneys and hemorrhage, edema and hyperemia in brain, respectively.