The present study was conducted to investigate the effect of Padina astraulis pretreatment on the gill and liver tissues of common carp (Cyprinus carpio) exposed to ZnO nanoparticles. A totalof 250 fish, weighing 20±2.4 g, were distributed in to 5 treatments, including no algae (treatment 1, control), diet containing 0.5% algae (treatment 2), 1% algae (treatment 3) and 2% algae (treatment 4), each treatment in triplicates and fed 3% body weight for 42 days. Upon finishing feeding trial, fish were exposed to 50% lethal concentration of zinc oxide nanoparticles for 14 days. The results of gill histopathology in nano-zinc-only treatments showed apical hyperplasia, basal hyperplasia, shortening of the epithelial gill glands, bending of the secondary lamella cells, and intense lamellar adhesion and these histopathologic alternations significantly decreased in those treatments with higher concentration of padina algae. Nano-zinc and algae significantly decreased with the elevation concentration of padina algae. In addition, nano-zinc treatments were caused tissue damage such as atrophy, biliary edema, sinusoidal inflammation, hemorrhage, hemorrhage, and flooding, and cloudy deformity in the liver, however, these effects were observed in nano and algae combination treatments, but their severity decreased with increasing the concentrations of padina algae. It can be concluded that application of Padina algae can play an effective role in reducing tissue lesions (liver and gill) in exposure to zinc nanoparticles.