The beta-nucleating activity and toughening effect of acrylonitrile-butadiene-styrene (ABS) graft copolymer on isotactic polypropylene (iPP) and the compatibilizing role of maleic anhydride grafted polypropylene (PP-g-MAH) on the iPP/ABS blends were investigated. The results show that ABS can induce the formation of beta-crystal in iPP, and its beta-nucleating efficiency depends on its concentration and dispersibility. The relative content of beta-crystal form is up to 36.19% with the addition of 2% ABS. The tensile and impact properties of the iPP were dramatically enhanced by introducing ABS. The incorporation of PP-g-MAH into the iPP/ABS blends inhibits the formation of beta-crystal. The crystallization peaks of the blends shift toward higher temperature, due to the heterogeneous nucleation effect of PP-g-MAH on iPP. The toughness of iPP/ABS blends improved due to favorable interfacial interaction resulting from the compatibilization of PP-g-MAH is significantly better than the beta-crystal toughening effect induced by ABS. POLYM. ENG. SCI., 59:E317-E326, 2019. (c) 2019 Society of Plastics Engineers