The high crystallization rate has some disadvantages that results in a narrower operating temperature region and it often makes the polymer processing difficult. Low crystallinity polypropylene (LCPP) was recently developed and has been used to improve the formability of polypropylenes PP) in their polymer processing processes, especially, the spinning processes by taking advantage of the fact that blending LCPP with isotactic PP (iPP) retards the crystallization kinetics of iPP. This study was concerned with the isothermal and non-isothermal crystallization behaviors of iPP / LCPP blends. The fast scanning chip-calorimetry (FSC) was used for the blends with different ratios so as to investigate the effect of LCPP on PP crystallization behavior. FSC enables the differential scanning calorimetry (DSC) measurement with high cooling rate and large degree of supercooling. The isothermal crystallization analysis was conducted in the temperature range from 0 to 110ºC. The non-isothermal analysis was conducted under high and constant cooling rate from 10 K/s to 1000 K/s. The Isothermal crystallization analysis elucidated that LCPP retards crystallization kinetics especially in the range between 10ºC and 40 °C. Furthermore, this retardation effect increased as the blending ratio of LCPP increased. With higher cooling rates than - 90 K /s, the double crystallization peak was observed in the cooling curves of iPP / LCPP blends. The peak-top temperatures, Tc_high and Tc_low, were calculated from double crystallization peaks measured at various cooling rates. Blending LCPP had little effect on Tc_high, but, Tc_low was shifted significantly to lower temperature with the increase of blending ratio of LCPP.