The effect of a commercial grade polyester thermoplastic elastomer (HY) on the crystallization behavior of a polyketone terpolymer of ethylene, propylene and carbon monoxide (EPCO) was investigated in terms of shear rate, temperature and blend composition. HY retarded the isothermal crystallization of EPCO in the static state. As the HY content increased, the half-time for the crystallization of the EPCO/HY blends increased, and the cold crystallization temperature (Tc) decreased. In addition, the average value of the Avrami exponent decreased, but the crystallization rate constant increased. The retardation of crystallization could be explained by steric hindrance or a shield effect of the HY phase on the growth of EPCO spherulites at a temperature near the Tc. HY also retarded the crystallization of EPCO in the dynamic state. However, the induction time of the blends was slightly decreased by increasing the magnitude of shear rate up to 10 rad s − 1. X-ray diffraction revealed that the introduction of HY had little influence on the crystal structure of EPCO.