ABSTRACTBackground and Objectives: This study investigated the coagulation of soymilk using fermented soy whey (FSW), a tradi-tional natural coagulant for tofu production. We comprehensively evaluated the effects of key parameters of FSW pH, FSWaddition amount, and FSW temperature on the physicochemical properties of the resulting tofu. Analyses included tofu yield,moisture content, water‐holding capacity, textural, sensory profile, and protein subunit composition via SDS‐PAGE. Experi-ments were conducted under controlled conditions, varying the FSW pH (3.78–4.50; 25% addition, 75°C), the FSW additionamount (17.5%–30% v/v; pH 4.0, 75°C), and the FSW temperature (35°C–85°C; pH 4.0, 25%).Findings: Protein aggregation efficiency increased markedly as FSW pH decreased, reaching a maximum at pH 4.02.Increasing the FSW concentration enhanced tofu yield and water retention up to 22.5% (v/v), while higher levels caused slightdeclines. Similarly, coagulation improved with rising FSW temperature, peaking at 65°C, where a cohesive gel with optimaltexture was formed.Conclusions: Therefore, the optimal parameters were identified as an FSW pH of 4.02, a concentration of 22.5% (v/v), and anFSW addition temperature of 65°C.Significance and Novelty: These parameters provide a scientific foundation for standardizing the traditional FSW tofu‐making process, offering crucial benchmarks for quality control and future product development.