The composition and physical nature of milk is very complex. The stability of milk depends upon the different constituent of milk. Determination of heat stability of milk is one of the factors that assess the stability of milk. In this study an attempt was made to measure the heat stability of milk obtained from different varieties of cows and also made an attempt to identify the different components on heat stability. The genetic variants and protein concentration of casein in the milk of six different varieties of cows were evaluated. The protein concentration in inbreed varieties are more than that of others followed by Holstein and Holstein-Friesian was found least. We also found that the concentration of casein was highest in inbreed varieties followed by Holstein and was least in Holstein-Friesian. The heat stability was maximum in Swiss Brown followed by inbreed and was least in Holstein-Jersey and Holstein. Lactose concentration was maximum in inbreed varieties followed by Sindhi cross and was least in Swiss Brown. Calcium concentration in inbreed variety was found to be maximum followed by Holstein, however, least was found in Swiss Brown. In Holstein varieties, the potassium concentration was found to be maximum, however the concentration was least in inbreeds. We did not find much difference in the pH and specific gravities of milk in various varieties.