This research was carried out to investigate polymorphisms of Myostatin gene in Holstein Friesians and Brown Swiss cattle breeds. PCR-RFLP methods were used to investigate of MSTN gene. DraI restriction enzyme were used to detected of MSTN gene polymorphism. The result showed that there were two genotypes (AA and AB) of MSTN gene in two cattle breeds. The allele frequencies in Holstein Friesians was 0.97 and 0.3. while The allele frequencies in brown swiss was 0.88 and 0.12. This result can be used in the future to improve meat properties and growth characteristics in the cattle breeds.