Based on the experimental results presented in Part I of this research, a three-parameter nonlinear constitutive model has been proposed to describe the strain rate and temperature dependent tensile behaviors of unfilled and talc-filled polypropylene. One of the parameters is the elastic modulus. The other two parameters in this model are a strain exponent, m, and a compliance factor, beta. Their relationships to strain rate and temperature are obtained from the experimental results. The simulated stress-strain curves from the model are in good agreement with the test data. The analysis of the model shows that the strain exponent m, which controls the strain softening (or hardening) effect of the material, is not only strain rate independent, but also temperature independent. The compliance parameter, beta which controls the flow stress level of the material, on the other hand, varies with both strain rate as well as temperature. Results also show that the addition of talc filler in polypropylene reduces the strain exponent m, and increase the compliance parameter, beta, which reduces the flow stress level of talc-filled polypropylene to lower than that of unfilled polypropylene.