Abstract: Epoxidized cottonseed oil was synthesized by reaction of organic acid acidified cottonseed oil with hydrogen peroxide using H3PO4 as catalyst in the emulsion system without solvent . The structure of synthesized epoxidized cottonseed oil was characterized by means of’ 1H NMR and FT-IR. Epoxy value，iodine value，acid value，and color of the product were determined by Chinese national standards. The effects of emulsiofier and organic acid，reaction time，temperature and proportion of reactants on the product properties were investigated. High quality epoxidized cottonseed oil plasticizer could be obtained by reaction of formic acid acidified cottonseed oil with hydrogen peroxide using MOA-3 as emulsifier without solvent. Epoxy value，iodine value (100g ) and acid value of the product could reach 6.12%、3.67g and 0.32 mg/g respectively. Epoxidized soybean oil was also successfully synthesized. The process avoids using organic solvent and decreases undesirable byproduct，and improves the quality of product.