Defatted soy flour (DSF) is an abundant renewable commodity and is more economically favorable then soy protein isolate or soy protein concentrate. DSF contains soy protein, soy carbohydrate, and soy whey. The aqueous dispersion of DSF was blended with styrene-butadiene latex to form elastomer composites. The inclusion of soy carbohydrate increased the tensile stress in the small strain region, but reduced the elongation at break. The shear elastic modulus of the composites showed an increase in the small strain region, consistent with its stress-strain behavior. The inclusion of soy carbohydrate and soy whey also improved the recovery behavior in the nonlinear region. At small strain, the shear elastic modulus of 30 % filled composites at 140 degrees C was about 500 times higher than that of the unfilled elastomer, indicating a significant reinforcement effect generated by DSF. Compared with soy protein isolate (SPI), the stress softening effect and recovery behavior under dynamic strain indicate the addition of soy carbohydrate and soy whey may have increased the filler-rubber interaction. In general, the DSF composites gave better mechanical properties compared with the protein composites. (c) 2005 Wiley Periodicals, Inc.