A series of stable waterborne polyurethane for leather finishing modified with epoxy resin and castor oil (ECOWPU) were prepared by the prepolymer process using polypropylene glycol (PPG) and isophorone diisocyanate (IPDI), with castor oil (CO) and epoxy resin(E-44) as the coupling agent. The structure of the polymer and the properties of the resulting films were analyzed by FTIR, TEM, DSC and TGA. FTIR showed that castor oil and epoxy resin were chemically incorporated into the copolymer. Both hydroxyl groups and epoxy groups of epoxy resin participated in the reaction. TEM showed that the particle morphology was spherical, and the particle size was relatively uniform. DSC indicated that the degree of micro-phase separation in the modified films increased. TGA revealed that the thermal properties were better when castor oil and epoxy resin were incorporated. With increase of the content of castor oil and E-44, the tensile strength increased asymptotically, and the elongation at break and the water absorption decreased.