In this study the rainbow trout (Oncorhynchus mykiss) myostatin gene (MSTN) for detecting gene derived SNPs and performing genetic association study between MSTN polymorphisms and growth traits were analyzed. Twenty broodstocks of rainbow trout in Genetic and Breeding for coldwater Fishes center in Yasouj for generating full sibling were selected and tagged and then juveniles were raised at the ponds until 5 months post-hatching. DNA extract based on standard method and these individuals selected randomly for molecular analysis. Two single nucleotide polymorphisms (SNPs: g.660T>C and g.1904C>A) in intron 1 and 2 regions of the MSTN gene in rainbow trout by were identified DNA sequencing and polymerase chain reaction single-stranded conformational polymorphism (PCR-SSCP) methods. The assessment results demonstrated that 6 haplotypes were revealed in this center. Moreover, association analysis indicated that the genotypes of SNP g.1904C>A are associated with the length and body weight at 90 and 150 days of age (P< 0.05), whereas no significant association was found between the SNP g.660T>C and growth traits. Our results provided evidence that SNPs in MSTN gene may be associated with length and body weight at fingerling age and MSTN gene may be used as potential candidate gene for marker-assisted selection (MAS) in rainbow trout breeding program