The crystallization and melting behavior are closely related not only to the external conditions such as undercooling and cooling rate, but also to the chain structure characteristics such as isotacticity distribution. The isotacticity distribution of three commercial isotactic polypropylenes (iPP) used in this work was characterized using Temperature-Rising Elution Fractionation (TREF) combining with Size-Exclusion Chromatography (SEC). Their crystallization and melting behavior were observed by Differential Scanning Calorimetry (DSC) and Polarized Light Microscopy (PLM). The results indicated that for iPP with similar molecular weight and isotacticity, the difference in isotacticity distribution not only led to the variation in nucleation and growth rates of crystal, but also changed the perfection of crystals formed under the same condition, even causing the formation of different crystalline modification and the change in the equilibrium melting temperature.