Abstract: Waterborne polyurethane(WPU) was prepared by the reaction of castor oil(C.O.) with polyether glycol(N 210),dimethoxypropionic acid(DMPA) and toluene diisocyanate(TDI).The effects of mass ratio of castor oil,N 210,DMPA content,molar ratios of NCO to OH and NH2/NCO on the properties were investigated.The structure of WPU was characterized by FT-IR.It was found that mechanical properties and water resistance of WPU coating film were increased with addition of castor oil.At 1:1-2 mass ratio of castor oil to N 210,1.6 molar ratio of NCO/OH,(5.5%) DMPA content and 0.50 molar ratio of NH2/NCO, the castor oil waterborne polyurethane has excellent film-forming property,high hardness,good resistances to water and petrol,and excellent adhesion to base materials.