To improve the crystallization and mechanical properties of poly(butylene succinate) (PBS), a series of poly(vinyl butyral) (PVBs) with various degrees of polymerization, have been synthesized as macromolecular nucleating agents. Nonisothermal crystallization kinetics of PBS nucleated by the PVBs has been examined via polarized optical microscopy and differential scanning calorimetry, followed by detailed analysis with theoretical models. The PVBs are found to significantly increase the number of spherulites and crystallization temperatures by 11 degrees C, and to reduce the spherulite size from 80 to 3 pm and the activation energy from 133 to 53 kJ/mol. Only Avrami and Tobin's models are capable of well characterizing the crystallization kinetics. The effects of the PVBs depend on their concentration and the degree of polymerization, coupled with their miscibility/immiscibility with PBS. Meanwhile, the nucleated PBS exhibits a significant enhancement in mechanical properties: 69% in Young's modulus, 26% in tensile strength, and 14% in impact strength.