Dynamic mechanical properties of ABS polymers with various rubber contents were measured in the glass transition temperature region of the rubber phase over a wide range of frequency. Time-temperature superposition could be applied well. The temperature dependence of the shift factors for all the ABS polymers was expressed by a common WLF equation with suitable choice of the reference temperature, Ts. log aT=-17.44 (T-Ts)/(51.6+T?Ts). The reference temperature was regarded as the glass transition temperature, Tg. Tg thus obtained decreased with a decrease in rubber content. Thermal stresses in ABS polymers estimated from the pressure dependence of Tgwere in good agreement with the theoretical values calculated from the difference in thermal expansion coefficient between the two phases and the rigidity, and increased with decrease of the rubber content. It was found that the two phases were bonded together with sufficient strength by grafted chains.