The crystalline structure of isotactic polypropylene/ ethylene-propylene rubber (iPP/EPR,85∶15,W/W) blends prepared by melt-blending and solution-blending methods,respectively was studied by using modulated differential scanning calorimetry (MDSC) and wide angle X-ray diffraction (WAXD).The experimental results reveal that α-iPP and β-iPP coexist in the PP85m sample prepared by melt-blending method,but only α-iPP appeared in the PP85s sample prepared by solution-blending method,and its crystalline structure is independent on isothermal crystallization temperature.The β-iPP content in PP85m is dependent on the crystallization temperature and approaches to a maximum at about 125℃.In addition,it is found that the iPP/EPR samples experienced annealing at 200℃ for different times(5～30 min)demonstrate the same melting behavior,indicating that the annealing treatment for different times at 200℃ has little effect on the formation of β-iPP in PP85m samples.It is suggested that the formation of β-iPP in PP/EPR blends is dependent on its thermomechanical history.