In this study, a low-fat Cheddar cheese was developed using polymerized whey protein (PWP) as a fat replacer and Lactobacillus helveticus as an auxiliary culture, and the effects of PWP on the physicochemical properties of cheese were studied. Results showed that addition of PWP and Lactobacillus helveticus increased the contents of moisture, protein, free amino acids and volatile compounds and lactic acid bacterial population, and markedly improved sensory characteristics and acceptance of cheese. Addition of PWP reduced the fat ripening period, and increased pH 4.6-soluble nitrogen (SN) fraction by 9.45% and 12 g/100 mL trichloracetic acid (TCA)-SN fraction by 11.74% after ripening. Cheese yield was not affected by adding PWP or the auxiliary culture. All the data indicated that polymerized whey protein can be used as a promising fat replacer for developing low-fat Cheddar cheese with good texture and sensory properties.