In last decade molecular marker information has been directly used in animal breeding programmes. It is expected that molecular markers could speed up the rate of genetic improvement by up to 30% (Kashi et al. 1990). Genetic markers which are related to genes and traits of interest could be used as a marker for selection. It is obvious that milk and reproduction traits are controlled by many genes. However, finding a candidate gene as a genetic marker which may have good influence for increase milk yield is quite important in dairy breeding industry. Some of genetic polymorphism in candidate genes which have significant effects on production traits is widely used. In this study Pit-1 transcription factor gene was used as a candidate gene. Transcription factor Pit-1 gene positively regulates the expression of growth hormone, prolactin and thyrotrophin-beta subunit genes (Zhao et al. 2004). It also plays a role in pituitary cell differentiation and proliferation. The aims of this study were to find the role of Pit-1 polymorphism on milk yield, fat and protein percentage and to study the usage of Pit-1 gene as a candidate gene for milk production traits in dairy cattle.