The study was conducted to find the association of αS1-casein locus with the milk performance traits in Sahiwal cattle. The identification of genotypes of αS1-casein locus was made with ARMS-PCR in 107 Sahiwal cows maintained in NDRI, Karnal. The association of genotypes with milk production traits was carried out using least square analysis with two-way classification of ANOVA after adjustment of data for non-genetic factor i.e. parity. The C allele was found in higher frequency (0.61±0.04) than that of B allele (0.39±0.04) in the population. Among the αS1-casein genotypes, CC was observed in 54 (0.50) animals whereas BC genotype was observed in 22 (0.21) animals. The genotype BB was found in 31 (0.29) animals in the population. The αS1-casein genotypes showed a non-significant (P<0.05) effect on all the parameters under study viz. milk fat %, SNF%, SNF yield and milk yield. The αS1-casein locus is less informative in the selection of animals for higher yields of fat, SNF and milk in the population under study since there was no effect of genotypes in milk performance traits