ABCG2 protein or Breast Cancer Resistant Protein (Bcrp), located in membrane of mammary glands alveolar epithelial cells, is one of the most important active transport proteins and responsible for passing of drugs from blood to milk. It is encoded by ABCG2 (Bcrp). These transport proteins are very important for veterinary medicine. Single nucleotide polymorphism, which is caused by changing amino acid (Y581S), in ABCG2 gene that encodes Bcrp, affect milk yield and milk properties in Israeli Holstein. It is known that fat and protein proportion in milk were increased, but milk yield was decreased in Israeli Holstein which have ABCG2(A) allele. In this study, allele frequency of ABCG2 was investigated in Holstein cows of Turkey and for this purpose 207 Holstein cows from Trakya region were genotyped. A allele (0.9807) had been found dominant in all investigated animals. C allele (0.0193) had been determined at only 8 animals. On the other hand CC homozygous had not been found in investigated animals.