A polypropylene/poly(ethylene-co-propylene) (iPP/EPR) in-situ blend synthesized by spherical Ziegler-Natta catalyst was fractionated by temperature-gradient extraction fractionation. The fractions were characterized using FTIR, C-13 NMR, DSC and WAXD. The in-situ blend was found to contain mainly three portions: an ethylene-propylene random copolymer, a series of segmented copolymer with PE and PP segments of different length, and propylene homopolymer. The impact strength of in-situ blends of different structural heterogeneity was measured, and the results show that increasing the amount of segmented copolymer has a positive effect on the impact strength. The segmented copolymer portion alone is found to increase the impact strength at room temperature greatly, while the low temperature impact strength can be markedly enhanced only when random copolymer coexists with the segmented copolymer.