Effects of the isothermal crystallization temperatures of poly(vinylidene fluoride), TIC,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 TIC,PVDF. Lower TIC,PVDF (e.g., 80 °C) facilitates the formation of PBA α crystals in both the isothermal and nonisothermal melt crystallizations and also favors the β-to-α phase transition of PBA upon annealing at elevated temperatures. This might be attributable to the decreased equilibrium melting temperature of PBA when TIC,PVDF is decreased. Higher TIC,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 TIC,PVDF than those with a higher TIC,PVDF, attributable to the preferential formation of α crystals at a lower TIC,PVDF. This study provides a new method to control the crystal modification and physical properties of polymorphic polymers in their blend systems.