Poly(propylene carbonate) (PPC) is an environmental friendly thermoplastic aliphatic polycarbonate. In order to improve its thermal and mechanical properties, PPC end-capped with maleic anhydride (PPC-MA) was prepared by reactive extrusion. Structure, thermal, and mechanical properties and rheological behavior of PPC-MA were investigated. FTIR results show that PPC was successfully end-capped with MA. It revealed that tensile strength, 596 weight loss temperatures, storage modulus, loss modulus, and complex viscosity were dependent on End-Capped Efficiency (ECE) and molecular weight of PPC-MA. When the MA content ranged from 0.5 to 1 phr, ECE and molecular weight increased. The decreases of ECE and molecular weight occurred as the MA content increased to 3 phr. The rheological responses of PPC-MA were used to characterize the mechanism of ECE with different MA content. When the MA content increased, shear viscosity of PPC-MA decreased. As a result, the residence time in reactive extrusion decreased and lead to the reduction of ECE.