The study was conducted to find the association of b-Lactoglobulin locus with the milk performance traits in 157 lactating Sahiwal cows maintained at Cattle yard, NDRI, Karnal. Two different variants of b-Lactoglobulin were detected from DNA by PCR-RFLP. It was found that the frequency of B allele was predominantly high (0.84±0.03) than that of A allele (0.16±0.03) in the population studied. Among the genotypes, BB was observed in 106 animals, whereas AB in 51 animals only. The genotype AA was not found in any of the animals. The statistical analysis showed non-significant effect of b-lactoglobulin genotypes on milk yield, milk fat percentage, SNF percentage, milk fat yield and milk SNF yield. Therefore, b-lactoglobulin locus was less informative in the selection of animals for higher yields of fat, SNF and milk. DNA based markers were of the better choice since animals could be screened at very early age instead of waiting for animals to come in milk.