The studies were carried out with milk from lowland cows of the Red-and-White breed in the second and fourth lactations and 8 to 12 wk after calving. Supplementation of diet of cows with the preparations containing rumen-pro- tected methionine and lysine (Smartamine™ML and Smartamine™M) was found to improve the processing quality of milk regarding its suitability for cheese- making. This was evidenced by the results of the Schern's test and analysis of such characteristics of rennet gel of casein as hardness, cohesiveness, and springiness. Similar activity towards improving the quality of milk and rheological characteristics of rennet gel was observed for the preparation containing only rumen-protected methionine (Smartamine™M). At the same time, the supplementation of diet of cows with rumen-protected amino acids was proven to adversely affect the heat stability of milk.