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Beta-casein gene (CSN2) is considered a marker of milk production traits in dairy cattle. Allele A2, the most common in Holstein-Friesian breed, is beneficial for milk protein yield. However, within CSN2 other mutations occur which could potentially be involved in shaping the variation of milk production traits. In this study a new SNP (C/T) was found located within a regulatory sequence of CSN2 (position-1578), called enhancer which is thought to play an important role in the amount of the beta-casein mRNA produced. The aim of the study was to verify effects of both SNPs on milk production traits in Polish Holstein-Friesian (HF) dairy cattle. Six-hundred-and-fifty bulls were genotyped with two methods, PCR-ACRS (Amplification-Created Restriction Site, Mph1103 I) and PCR-RFLP (EcoR I), for the A1/A2 polymorphism and the C/T SNP polymorphism (BCE129), respectively. Although both SNPs are located close to each other, their allele frequencies were found significantly different (0.33, 0.67, 0.89 and 0.11 for the A1, A2, C and T, respectively). A mixed linear model was used for testing the association between these polymorphisms and deregressed breeding values for production traits. The analysis revealed that the allele coding the A2 protein variant increases breeding values for milk and milk protein yields while allele C of BCE129 increases the milk fat yield.