The aim of the study was to analyse the relationship between the Arg4Cys and Ala59Val polymorphisms of the bovine leptin gene, and the milk traits, based on the breeding values of AI proven bulls. A total of 187 individuals was analysed. The following allele frequencies have been found: 0.55 (C) and 0.45 (T) for Arg4Cys, and 0.73 (C) and 0.27 (T) for Ala59Val. Arg4Cys TT genotype has a highly significant increasing effect on milk yield and a significant increasing effect on protein yield, whereas no marked influence of this polymorphism can be observed on butterfat yield. Consequently, the content of butterfat is highly significantly decreased by genotype TT. In contrast, Ala59Val does not affect amounts of milk and protein, but is responsible for controlling the amount of produced butterfat.