Abstract: In this study, DNA isolated from blood samples of Iranian Holstein cows (N = 120) and PCR products (156 bp) were analyzed by SSCP technique with MDE gel. Then 4 patterns (Z1, Z2, ...Z4) of provided by SSCP were sequenced and then using POLYPHRED 5.04 software, 4 SNPs were detected in positions 6237, 6263, 6268 and 6297. The genotypes were TC and TG in position 6237, TT in position 6263, AG in position 6268 and AC in position 6297. From of detected SNPs, they that located in positions 6237 and 6268 caused change in the amino acids sequence of protein. These data provide evidence that bPRL gene is a good polymorphic source for single nucleotides that can be used for association with milk yield and investigate whether mutations in this sequences might be responsible for quantitative variations in milk yield and composition.