Elongational flow behavior of ABS polymer melts with various rubber‐particle contents was investigated by using a Meissner‐type uniaxial extensional rheometer. The effects of strain rate and rubber particles on the elongational behavior are discussed. A linear viscoelastic behavior was observed at sufficiently low strain rates ε̇. The dependence of linear elongational viscosity η+E(t) on particle content is weak at short times but becomes stronger with time. Two types of mechanisms which cause the deviation of nonlinear viscosity function η+E(t,ε̇) from η+E(t) at high strain rates in the short and long time regions were proposed. These deviations are respectively attributed to a volumetric resistance against the radial deformation of the samples because of the existence of particles, and an extension of matrix polymers in an elongational flow field.