The toughness behavior of PPO-SAN blends with the modifier poly(styrene-block-butadiene) (SBSB) and with poly(styrene-block-butadiene-block-methyl methacrylate) copolymers (SBM) under impact loading conditions has been investigated. The observed morphology of blends compatibilized with SBM, in which the rubber phase discontinuously accumulated at the PPO-SAN interface, correlated with about 20 times higher energy dissipation up to maximum force and about seven times higher deformation capacity compared to pure PPO-SAN blends. In contrast, the fracture behavior of the SBSB-modified blends was not as strongly dependent on the rubber content. It is especially noteworthy that although the SBM modification resulted in a strong increase in toughness of the PPO-SAN blends, no decrease in stiffness could be found with up to 15% rubber additions. The values of Young's moduli remained at the same high level of the nonmodified material.