The poly(3-hydroxbutyrate-co-3-hydroxyvalerate)/poly (g-caprolactone) block copolymers (PHCLs) with three different weight ratios of PCL blocks (38%, named PHCL-38; 53%, named PHCL-53; and 60%, named PHCL-60) were synthesized by using PHBV with two hydroxyl end groups to initiate ring-opening polymerization of g-caprolactone. During DSC cooling process, melt crystallization of PHCL-53 at relatively high cooling rates (9, 12, and 15 degrees C min(-1)) and PHCL-60 at all the selected cooling rates corresponded to PCL blocks so that PHCL-53 and PHCL-60 were used to study the nonisothermal crystallization behaviors of PCL blocks. The kinetics of PCL blocks in PHCL-53 and PHCL-60 under nonisothermal crystallization conditions were analyzed by Mo equation. Mo equation was successful in describing the nonisothermal crystallization kinetics of PCL blocks in PHCLs. Crystallization activation energy were estimated using Kissinger's method. The results of kinetic parameters showed that both blocks crystallized more difficultly than corresponding homopolymers. With the increase of PCL content, the crystallization rate of PCL block increased gradually. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2288-2295, 2010