Crystallization behavior of blends of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and poly(epsilon-caprolactone) (PCL) prepared by solution casting has been investigated by differential scanning calorimetry (DSC). In the study of PHBV/PCL blends by DSC, crystallization temperature of PHBV in the blends decreased about 8-12 degrees. From the results of the Avrami analysis of PHBV in the PHBV/PCL blends, crystallization rate constant of PHBV in the PHBV/PCL blends decreased compared to that of the pure PHBV. From the above results, it is suggested that nucleation of PHBV in the blends is suppressed by the addition of PCL. From the measured crystallization half time and degree of supercooling, interfacial free energy for the formation of heterogeneous nuclei of PHBV in the PHBV/PCL blends was calculated and found to be 2360 (mN/m)(3) for the pure PHBV and 3090-3160 (mN/m)(3) for the blends. This increase in the interfacial free energy of PHBV indicates that the heterogeneity of PHBV in the PHBV/PCL blends is deactivated by the PCL. This result is consistent with the result of crystallization rate constant of PHBV in the blends.