The effects of preexisting poly(butylene succinate-co-24 mol % hexamethylene succinate) (PBHS) crystals on the crystallization behavior and crystalline morphology of poly(butylene adipate) (PBA) were studied in their fully biodegradable melt-miscible crystalline/crystalline blend. Regardless of crystallization conditions, PBHS crystallized first, and PBA must crystallize in the presence of preexisting PBHS crystals. The preexisting PBHS crystals may not only enhance the nonisothermal melt crystallization behavior but also favor the nucleation and growth of only alpha-form crystals of PBA, providing an easy method of controlling the polymorphic crystals of PBA through polymer blending; moreover, the preexisting PBHS crystals could accelerate the overall isothermal melt crystallization process of PBA in the blend. PBA must crystallize as tiny crystals at the same orientation as the crystallites of the host PBHS spherulites in the blend, unlike the spherulitic morphology in its neat state. Both components crystallized separately according to their own crystal structures in the blend.