To utilize Soy Protein Isolate (SPI)–starch complexes in cooking Japanese-style Nimono stews , the NaCl diffusion coefficient D was measured and the cooking conditions were examined using a 15％-SPI–7.5％-starch gel, a 22.5％-SPI gel, and a 22.5％-starch gel. The D in the SPI–starch mixture gel was almost the same as that of the starch gel and about twice that of the SPI gel. The three kinds of gels did not collapse even when they were heated at 98℃ for 60 min. The hardness of the SPI–starch mixture gel was almost the same as that of the starch gel, but was lower than the SPI gel and showed no appreciable changes during heating at 98℃ in a NaCl solution. In addition, the predicted value of the NaCl concentration of the three kinds of gel heated at 98℃ was in good agreement with the measured value.