Thermal treatment has been utilized to improve the functional properties of proteins for many years. In this study, we aimed to investigate the effect of sodium triphosphate (Na₅P₃O₁₀) on particle size and size distribution of heat‐induced whey protein concentrate (WPC) aggregates under different processing conditions. The results showed that high Na₅P₃O₁₀ level (>0.5%, w/w), long heating time (>15 min), and alkaline condition (pH 8–8.5) facilitated formation of large particles (>10 μm). The WPC aggregates with small‐to‐medium particle size (1–3 μm) that are suitable to be applied as a fat replacer were obtained by heating the WPC solution (8%, w/v) containing 0.4% (w/w) Na₅P₃O₁₀ at 85°C for 5 min. We conclude that thermal treatment of whey protein concentrate added with Na₅P₃O₁₀ can obtain whey protein products with different particle sizes for certain applications.