The present study was conducted to assess the influence of dietary manganese sulfate nanoparticles on the growth performance, hematology, and blood biochemistry of rainbow trout (Oncorhynchus mykiss). 240 rainbow trout with an average initial weight of 0.8±0.1gr distributed into four treatments with three replicates and were fed with four diets including a control diet (without manganese), Mn-M (containing 10mg/kg manganese sulfate), Mn-N10 (containing 10mg/kg nano manganese), Mn-N15 (containing 15mg/kg nano manganese) for 6 weeks. The fish were hand-fed to satiation four times daily. At the end of the experiment, the average final weight of fish fed diets containing nano Manganese were significantly higher compared to control treatment (p<0.05), however, there was no significant difference compared to the group fed with manganese sulfate (p>0.05). Condition factor (CF) in juveniles fed diets containing Mn sulfate nanoparticles did not show a significant difference compared to those fed with manganese sulfate (Mn-M; p>0.05). The levels of hemoglobin (Hb) in fish fed Mn-N10 diet was significantly higher than fish fed with the control diet. Fish fed diets Mn-N10 and Mn-N15 showed higher plasma albumin compared to the control and Mn-M diets. In general, the results of this study showed that dietary supplementation of manganese sulfate nanoparticles compared to manganese sulfate had no significant impact on growth performance, hematological and biochemical composition of rainbow trout.