Inspired by the epitaxial crystallization theory and isomorphism phenomenon, poly(omega-pentadecalactone) (PPDL) and the random copolyesters of w-pentadecalactone and E-caprolactone Poly(PDL-co-CL)s have been synthesized and tested as polymeric nucleating agents for commercial poly(epsilon-caprolactone) (PCL). Crystallization behavior and spherulite structure of the neat PCL and nucleated PCL specimens have been investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and atomic force microscopy (AFM). The PPDL and poly(PDL-co-CL)s are found to provide massive heterogeneous nuclei, significantly increase the crystallization temperature to 314.2 K at a cooling rate of 10 K/min, and exhibit a supernucleation role in the PCL matrix. Moreover, investigation on crystallization kinetics demonstrates that the greatly enhanced nucleation dominates the overall kinetics. The enhanced crystallization ability of PCL and the polymeric nature of additive PPDL lead to a 12.4% improvement in tensile strength, without any loss of elongation at break. Three characteristics of perfect lattice matching, good surface wettability, and strong crystallization ability are suggested to guarantee the supernucleation effect of PPDL in the PCL matrix.