Polyunsaturated fatty acid (PUFA) was separated from rubber seed oil (RSO)，and then epoxidized PUFA (EPUFA) was prepared by peroxyacetic acid generated in situ by reacting acetic acid and hydrogen peroxide with PUFA from RSO. Influence of the amount of 30 % H₂O₂ and acetic acid，reaction time，and reaction temperature on epoxidation were studied，results showed that the optimum reaction conditions as follows：the ration of PUFA/acetic acid / 30 % H₂O₂ was 1/0.9/2.5 (g/g/g)，the mixture reacted under 65 ℃ for 3 h，the epoxy value of EPUFA was up to 8.28 mol/100 g，relative conversion to oxirane was 82 %，conversion of double was 97 %.