This study was conducted to investigate the effect of soybean protein isolate (SPI) on the baking qualities of bread which was made of composite flour blended with SPI extracted at acidic (pH 2.0, 3.0), neutral (pH 7.0) and alkaline (pH 10.0, 12.0) conditions. The mixogram showed that water absorption of composite flour dough blended with SPI extracted at pH 2.0 and 12.0 was higher than that of 100% wheat flour dough, and mixing time was shorter than that of 100% wheat flour dough. No differences were found between the composite flour blended with SPI at level of 5% and 100% wheat flour on the loaf volume of bread. The loaf volume of bread made of composite flour blended with at level of 10% was lower than that of 100% wheat flour, but that of , which had higher emulsion capacity than was similar to that of 100% wheat flour. No differences were found between the composite flour blended with SPI at level of 5% and that of 100% wheat flour on springiness, chewiness, cohesiveness, gumminess, adhesiveness and hardness of bread. The composite flour blended with SPI at level of 10% was similar to 100% wheat flour on springiness, chewiness, cohesiveness, gumminess, adhesiveness and hardness of bread except for chewiness, gumminess and hardness of which were significantly higher than that of 100% wheat flour (P