Poly(butylene succinate)/magnesium hydroxide sulfate hydrate whisker (MHSH) composites were prepared using the prepolymer from 1,4-butanediol, succinic acid, and modified MHSH, which were characterized by FTIR and H-1 NMR. The thermal, crystallographic, and mechanical properties of the PBS composites were investigated. Differential scanning calorimetry (DSC) demonstrated that glass transition temperature (T-g) and crystallization temperature (T-c) were increased with increasing of filler content. The thermal degradation process of PBS composites was analyzed by TG-FTIR, and a possible thermal degradation mechanism of PBS was proposed. The results indicated that the prepolymer was better than UMHSH in interfacial adhesion with PBS: The tensile strength, flexural strength, and modulus were significantly increased with the addition of filler mass fraction, especially when the composites were blended with the prepolymer.