In the last decade molecular marker information has been directly used in animal breeding plans. It has been expected that molecular marker could speed up the rate of genetic trends up to 30%. Genetic markers which are related to genes and traits of interest could be used as a marker for selection. It is already stated that milk and reproduction traits are controlled by many genes. When the aim is selection by makers it is not necessary to map the quantitative trait loci. Finding makers related to the trait and selection on the basis of marker information could be enough. Then, finding a candidate gene as a genetic marker for increase milk yield is quite important in animal. Genetic polymorphism in candidate genes which has 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 ? subunit genes. It also plays a role in pituitary cell differentiation and proliferation. Association studies have shown that Pit-1 is associated with growth rate, carcass traits and milk production in domestic animals. In cattle Pit-1 was found to be associated with body weight, and milk, protein and fat yield. Therefore, the Pit-1 gene could be a good candidate gene for genetic markers for milk production traits in dairy cattle. Random blood samples of 262 cows from 4 different dairy farms in Isfahan province were collected for extracting DNA. Pedigree and yield information of sampled cows were collected from dairy farm database. In PCR reaction a part of Pit-1 gene (451 bp) was amplified. Amplified fragments were affected by Hin fI enzyme for digestion. Non digested fragment (451 bp) shows AA genotype while appearing of non digested (451 bp) as well as two digested fragments (244 bp and 207 bp) would be AB genotype. However, production of only two digested fragments (244 bp and 207 bp) will be BB genotype. Frequency of A and B alleles were 0.27 and 0.73, respectively. Genotypic frequencies of AA, AB and BB were calculated to be 0.04, 0.45 and 0.51, respectively. Genotypic frequencies of the collected samples for Pit-1 gene were in disagreement with Hardy-Weinberg equilibrium (p 0.01). Genotype was a significant source of variation for birth wt., days in milk, open days, and fat and protein percent (p 0.1) while gestation length, dry days, total milk yield (kg) and standard milk yield were not affected by genotype. Birth wt., dry days, fat and protein percentage were highly significant (p 0.01) and days in milk significantly (p 0.05) was influenced by Herd management but total milk yield (kg), standard milk yield, open day