Large deformation, nonlinear stress relaxation behavior was examined in the molten state for two types of ABS polymers, with one type containing well-dispersed rubber particles and the other, agglomerated rubber particles. These different morphologies were accomplished by adjusting the chemical composition of poly(styrene-cp-acrylonitrile) (SAN) grafted on the rubber particles, such that the acrylonitrile content of the grafted SAN is equal to or different from that of the matrix SAN. The time-strain separability was found for the nonlinear relaxation of the matirx/grafted SAN chains in those ABS polymers. In the ABS polymer containing randomly dispersed rubber particles, the damping function h(gamma) of the SAN chains was more strongly dependent on the strain gamma than h(gamma) of the pure matrix SAN chains. This difference was attributed to the filler effect in that ABS polymer. In contrast, in the ABS polymers containing networks of the agglomerated rubber particles, the SAN chains exhibited less gamma -dependent h(gamma) that is close to the pure matrix chains, possibly due to lack of the filler effect in large pockets formed in this network.