The enhancement effect of nucleation in immiscible blend systems has recently attracted interest Although several authors have reported that the effect occurs at the phase interface. little is known about the mechanism involved We focused oil poly(r-lactide) (PLLA)/poly(epsilon-carprolactone) (PCL) immiscible blend Systems in which the presence of PCL enhanced the nucleation of PLLA at low temperature. We investigated the nucleation behavior of PLLA during aging at temperatures below T, Generically, neat polymers, including 0 PLLA, seldom generate nuclei below T-g due to restrictions in chain mobility. However through DSC analysis of the crystallization behavior following an aging process, we revealed that the nucleation of PLLA occurs during aging even It temperatures below T-g in the PLLA/PCL blend Since the nuclei density became saturated with increasing aging time, the nucleation behavior wits regarded as heterogeneous nucleation. The asymptotic density of nuclerdepended oil the PCL content, indicating that dispersed PCL acted its active sites for nucleation The nucleation rate R was almost independent of the aging temperature, suggesting that the marked decrease in chain mobility due to the glass transition is locally evaded at the active sites Nucleation was observed even at temperatures as Much its 40 degrees C lower than T-g. following the addition of only I wt% PCL, while the T-g obtained by it DSC heating scan Showed it subtle decrease. This suggests that the limited miscibility of PLLA/PCL leads to the aggregation of PCL and induces local and deep depression of T-g, at the interface of the PCL domains, resulting in marked enhancement of PLLA nucleation