Poly (lactic acid) (PLA) and poly (butylene succinate) (PBS) were melt-blended combined with hexamethylene diisocyanate (HDI). It was investigated that how the HDI content effected the blends phase morphology, the mechanical properties and rheological behavior. The increase in the complex viscosities of the blends indicated that compatibilization of the blend had occurred. It was shown that the size of the dispersed phase decreasing with the HDI content increases and appearing the fibrillation connection between the PLA and PBS phases by scanning electron micrographs, indicating that HDI plays a compatibilizing role. The crystallization rate of PLA was accelerated by PBS and chemical cross-link points as nucleating agents. Due to the good interface compatibility between PLA and PBS and the increased crystallinity of PLA and PBS, the impact toughness of the annealed PLA/PBS/HDI blend was significantly improved.