Effects of the isothermal crystallization temperatures of poly(vinylidene fluoride), T-IC,T-PVDF, on polymorphic crystalline structure, phase transition, fractional crystallization, and enzymatic degradation of poly(butylene adipate) (PBA) in crystalline/crystalline blends have been investigated. The crystal modifications of PBA can be regulated by T-IC,T-PVDF. Lower T-IC,T-PVDF (e.g., 80 degrees C) facilitates the formation of PBA alpha crystals in both the isothermal and nonisothermal melt crystallizations and also favors the beta-to-alpha phase transition of PBA upon annealing at elevated temperatures. This might be attributable to the decreased equilibrium melting temperature of PBA when T-IC,T-PVDF is decreased. Higher T-IC,T-PVDF is favorable for the fractional crystallization of PBA, which tends to segregate in the interlamellar regions of the PVDF matrix under these conditions. PBA shows faster enzymatic degradation in the blends with a lower T-IC,T-PVDF than those with a higher T-IC,T-PVDF, attributable to the preferential formation of alpha crystals at a lower T-IC,T-PVDF. This study provides a new method to control the crystal modification and physical properties of polymorphic polymers in their blend systems.