According to Mendels Laws, genetic variations of major six milk proteins in ruminants were identified;asi casein, as 2 casein, ß casein, K casein, a-lactalbumin, ß-lactoglobulin. Polymorphisms were detected in the DNA region containing milk protein genes in ruminants. In this review, it is aimed to determine the milk protein genes which effect the milk production traits and milk quality.