Whey protein preparations namely UF-retentate, freeze-dried whey protein concentrate (WPC) and spray dried WPC, were investigated for their composition and thermal behavior at low pH. These preparations differed in their chemical constituents. The protein, lactose, fat and ash content of these preparations were in the range of 58.92–73.00%, 14.48–27.70%, 5.12–8.18% and 4.955.00%, respectively. Ultrafiltration procedure increased the protein and fat content in WPC significantly and simultaneously reduced levels of other constituents. Whey protein solutions (2% protein) made by dissolving these preparations exhibited maximum thermal stability at pH 3.5 and their stability decreased drastically above pH 4.0. Similarly soluble protein content was maximum at pH 3.5 and minimum at pH 4.5. UF-retentate showed highest thermal stability under acidic conditions followed by freeze dried WPC and spray dried WPC.