Thermoplastic polycarbonate modified polyether-polyurethane (PEPU) elastomers were prepared by transurethane polycondensation method using poly(oxytetramethylene) glycol of M n 5 2000 and dimethyl-hexane-1,6-dicarbamate as the main raw materials, 1,4-butanediol as a chain extender and polycarbonate diol (PCDL) as an additive in the presence of dibutyltin oxide as a catalyst. The effect of the PCDL on the PEPUs' structure, intrinsic viscosity, molecular weight, mechanical, optical, and thermal properties, and water resistance were studied. The polycarbonate modified PEPUs showed better mechanical and thermal properties, but lower molecular weight and optical properties than the PEPUs. The PEPUs modified by PCDL1000 exhibited better performance, including mechanical, optical, and thermal properties, than those by PCDL2000.