Abstract: Many factors who affect the stability of whey proteins treated by heating were studied over 2.5 to 8.5 pH range in differential scanning calorimetry using and heat-induced precipitation. Heating of whey proteins at 95°C for 5 min above pH 3.8 to 3.9 produced extensive of the protein coagulation. The highest denaturation temperature for an acid whey protein concentrate prepared by ultrafiltration was 88°C at pH 3.5, while for an isolated β-lactoglobulin preparation. The highest denaturation temperature, obtained also at pH 3.5 was 81.9°C. Presence of milk sugars (lactose, glucose and galactose) appeared to increase the resistance of β-lactoglobulin to thermal denaturation. Heat stability of α-lactalbumin was lower at pH 3.5 than in pH 6.5 to 4.5 range; at all pH denaturation temperatures of α-lactalbumin (61.5 to 58.6°C) were lower than those for β-lactoglobulin or two serum albumin preparations. Thermal behavior of an ultrafiltration whey protein concentrate appears to be controlled by the dominating β-lactoglobulin fraction.