The effect of thermal annealing on the mechanical properties and microstructure of polymers has been studied intensively. Nevertheless, sparse work investigated the influence of annealing on the mechanical properties of materials with alternated structure. In this work, the evolution of properties and microstructure of iPP samples with different structure after annealing were discussed. Note that annealing plays a little role on microstructure of all the specimens, whereas its effect on the variation of impact strength of different samples does not show the similar trend. For sample CIM and V1, impact fracture toughness does not improve significantly after annealing within the range of temperature used. But the promotion of the impact strength of sample V2 is extremely remarkable (from 29 KJ/m(2) to 90.5KJ/m(2)), which can be attributed to better interfacial adhesion, resulting in violent crack deflection and plastic deformation, the formation of microfibers and the better ability of load transfer.