A study was conducted to compare growth and nutrients in the muscle of diploid and triploid masu salmon (Oncorhynchus masou B., 1856). Triploidy was induced by providing a heat shock treatment to the fertilized eggs. When fish grew up to 100 g around, triploids were prepared after triploidy determination prior to the trial. Initial mean weights of diploids and triploids were 103.67 ± 9.66 g and 109.95 ± 8.45 g, respectively. Quadruplicate groups of 30 fish were randomly assigned in each tank fed by water with a flow-through system and were fed to apparent satiation for 140 days. Survival, specific growth rate, feed conversion rate, condition factor, relative growth rate and absolute growth rate were determined in both groups. The contents of moisture, crude protein, lipid, ash, amino acids and fatty acids in muscle were analyzed. It has been determined that the triploid fish showed a higher weight gain than diploid fish despite the difference was not significant (P>0.05). There were no significant differences in crude protein, crude lipid, ash, amino acids and fatty acids between diploids and triploids (P>0.05). In conclusion, growth performances and nutritional composition in muscle were similar between diploids and triploids, and triploids had no negative effects on muscle nutrients under fish farming practices especially for the production of Oncorhynchus masou on-growing stages.