Abstract: A series of plant-oil-based waterborne polyurethane (WPU) samples were synthesized using hydroxypropyl-terminated polydimethylsiloxane (HP-PDMS) and castor oil as raw materials by a prepolymer method. The different content of HP-PDMS was introduced into the polyurethane molecular chains to obtain the HP-PDMS/WPU hybrid composites through the chemical reaction between the OH groups on HP-PDMS and the NCO groups on IPDI. The hydrophobicity, thermal stability and mechanical properties of the composites were investigated by FTIR, TEM, thermal analysis, static contact angle and tensile experiment. The results indicated that the modified nanocomposites were synthesized successfully and their thermal degradation characteristic temperature at 5 % weight loss was enhanced from 225 ℃ to 248.5 ℃ due to the incorporation of HP-PDMS. Both the tensile strength and hydrophobicity of the composites could be fairly enhanced with the addition of small amounts of HP-PDMS.