We developed a method for mass production of rice protein isolate (RPI) and evaluated its nutritional quality in rats. To obtain thick slurry, rice flour was mixed with a 0.6% Termamyl 120L-solution (1:2, w/v) at room temperature (approximately 23 degrees C). The slurry was heated at 97 degrees C for 2 hr with stirring. Gelatinization and liquefaction occurred simultaneously. RPI obtained by filtration and washing with boiling water, was more than 90% pure protein (dry matter basis). It also contained 6.4% dietary fiber, 1.3% ash, and 1.1% carbohydrate. RPI diets (40-50%) allowed the maximum growth in rats comparable to that with 25% casein diet.