Wheat bran was substituted with cassava‐defatted toasted soy composite at 0, 10, and 20% substitution levels followed by extrusion cooking and some nutritional, functional, and rheological properties of the extrudates were determined. There was a significant (p < 0.05) increase in starch digestibility of composites after extrusion cooking, but the substitution of wheat bran lowered the rate and extent of starch hydrolysis. Extrusion cooking led to a reduction in NSI and IVPD. Substitution of cassava‐defatted toasted soy composite with wheat bran reduced expansion and solubility index of extrudates. Extrusion cooking also promoted fiber fragmentation with a consequent increase in soluble dietary fiber and a decrease in insoluble dietary fiber content. All the composites exhibited a shear thinning behavior and the composite with 20% wheat bran had the highest viscosity. The result indicates that substitution of starch with wheat bran together with extrusion cooking can be applied to produce products with improved nutritional and functional properties.