Abstract: Dehydrated castor oil(DCO) was firstly prepared by using castor oil(CTO) as raw material via dehydration reaction, and epoxidized dehydrated castor oil(EDCO) was synthesized using phosphoric acid as catalyst and acetic acid peroxide as the oxidant by epoxidation reaction afterwards. The influences of different parameters on the epoxy value of EDCO were investigated through single factor and orthogonal experiments. The results indicated that the optimal preparation conditions of EDCO were 3.5 h reaction time, 30 ℃ reaction temperature, 5.5:1 molar ratio of peracetic acid to DCO and 0.5％ phosphoric acid dosage. The epoxy value of EDCO could be up to 4.82% under these conditions. In addition, the chemical structures of CTO, DCO, and EDCO were characterized by FT-IR and 1H NMR . It was confirmed that the C=C double bonds in EDCO almost disappeared and the epoxy bonds were formed during the epoxidation. The properties of the products were also studied by viscosity measurement and thermogravimetric analysis(TG). Viscosity measurement showed that the viscosities of CTO, DCO, and EDCO were 1100.0, 299.5 and 1896.0 mPa·s, respectively. TG analysis demonstrated that the descending order of thermal stability of the products was EDCO> DCO> CTO.