The crystallization process of poly(is an element of-caprolactone)/oligostyrene (PCL/OS) blends was analyzed by measuring the spin-spin relaxation time T-2 by pulsed NMR. We examined: (i) the temporal changes of T2 and the fractional amount f of the crystalline, amorphous, and intermediate components in the primary and secondary crystallization processes; and (ii) the dependence of the behavior on the crystallization temperature T-c and the OS content phi(OS) The decrease of T-2 of the intermediate and amorphous components with increasing phi(OS) indicated that OS rejected during crystallization is mixed with the residual amorphous PCL as well as trapped in the interface between a lamellar crystal and an amorphous layer. The fraction of the crystal, which is the crystallinity based on the number of protons, decreased with increasing T-c. This is ascribed to the polydispersity of PCL. The values off of the crystalline and amorphous components depended less on T-c and phi(OS) after the secondary crystallization proceeded than at the end of the primary process. This indicates that the secondary crystallization has the effect of annealing. The fraction of the interface can be an index of regularity of the lamellar structure. Its change implied which process of lamellar thickening, lamella generation, and the rejection of OS was dominant in the secondary crystallization. We also discussed which region OS was rejected into. The changes off of the three components in the secondary process showed extreme values at phi(OS) similar or equal to 5%. To discuss this behavior, we proposed two possibilities, namely the influence of the morphology of the spherulites and local phase separation during crystallization.