Abstract: The intrinsic brittleness of polylactic acid (PLA) greatly restricts broader application in multiple fields, while the blending with elastomer is considered a feasible strategy to improve the ductility of PLA materials. Unfortunately, the poor compatibility of two phases needs to be solved. In this work, using diisophenyl peroxide (DCP) as reactive compatibilizer, PLA and poly(propylene carbonate) polyurethane (PPCU) were melt blended to prepare PPCU/PLA blends. The effects of DCP content on the phase morphology, rheological properties and mechanical properties of PPCU/PLA blends were investigated. The results demonstrated that DCP initiated the branched crosslinking reaction between PLA and PPCU molecular chains. With the increase of DCP content, the complex viscosity and storage modulus of PPCU/PLA blends also enhanced, indicating the reinforcement of elastic behavior, and the Cole-Cole plot indicates that when the DCP addition exceeds 0.3wt%, the blend exhibits high homogeneity. As the DCP content increases, the phase interface of the blend gradually becomes blurred, the dispersed phase size significantly decreases, and the phase morphology of the blend is improved. Meanwhile, the addition of DCP significantly enhance the elongation at break of the blends. The elongation at break of 0.2wt% DCP in PPCU/PLA increased to 224.37%, which was 10.68 times as high as that of the blends without adding DCP. Additionally, notched impact strength of PPCU/PLA blends increases with DCP addition. When 0.5wt% DCP was added into the blends, the impact strength of the blends is increased to 7.91 kJ/m², which is more than 2.94 times than the pure PPCU/PLA blends. The proposed modification strategy may be responsible for the enhancement of mechanical properties of PPCU/PLA blends, exhibiting the improvement of compatibility between the two phases.