Abstract: To make a comprehensive analysis, preparative temperature rising elution fractionation (pTREF) and preparative molar mass fractionation (pMMF) are adopted to fractionate the olefin block copolymers (OBC) into fractions with narrower branching and molar mass distributions, respectively. The chain structure and composition of the bulk resins as well as the corresponding pTREF and pMMF fractions are further analyzed by means of gel permeation chromatography, crystallization elution fractionation, and differential scanning calorimetry. The results indicated that the multiple fractionations are a type of powerful approach to generate a library of OBC samples. Such a library can be composed by the fractions with similar molar masses but different branching structures or by the fractions with similar branching but different molar masses. Furthermore, the cross-fractionation was performed for these sample libraries by comprehensive analytical techniques to provide in-depth information on the molecular heterogeneity of OBC samples.