Nano-technology is an in-progress new technology which has many effects on environment and living organisms. The aim of the present study was to compare the effects of zinc heavy metal and its nanoparticles on the gill tissue of Capoeta capoeta gracilis. Seventy fishes were caught from Zarin-Gol River in Golestan province. After treatment, they were grouped into zinc sulfate and nano zinc under four concentrations (5, 20, 40 and 100 ppm) in fourteen days and one treatment was set as the control. Samples were prepared from gill tissue after fixation in formalin. The observed gill lesions were strong and mediate for zinc sulfate and nano-zinc oxide, respectively which included: hiperpelasia, hiperthrophy, nechrose and lamellar fussions. Results revealed that the gill tissues which were exposed to zinc sulfate showed strong histopathological effects to control treatment. More complications were observed with the increase in zinc concentration, but samples that were exposed to nano-zinc, showed gradual histopathological effects with increase in concentration. Moreover, the histopathological effects of the gills exposed to nano zinc were less than those to zinc sulfate. In general, the nanoparticles have fewer adverse effects and are recommended for use in aquatic ecosystems industry