Nonlinear viscoelastic properties were measured in the molten state for two series of ABS polymers with rubber particle contents of 5, 10, 15, and 20 wt%. Experimental results for the shear relaxation modulusG(t,γ)obtained at large step strains revealed a striking fact that the strain dependence of the modulus disappears in the region where a long‐time relaxation due to the particles is dominant. In single‐step stress relaxation, theG(t,γ)curves are composed of two contributions, entanglement relaxation of the matrix polymer at shorter time scales and long‐time relaxation due to the particles. In order to separate the above two contributions, double‐step stress relaxation experiments were done in which the first step strain −γ is applied att=−t1and the second step strain γ is added att=0.It is shown thatt1should be comparable with the maximum relaxation time of the matrix polymer for proper evaluation of the particle contribution.