Epoxidation of dicyclopentadiene via phase transfer catalysis was successfully carried out in an acidic solution/organic solvent two-phase medium. The reaction is greatly enhanced in the presence of quaternary ammonium salt using hydrogen peroxide as the oxidizing agent, and sodium tungstate and phosphoric acid as the cocatalyst. Three products, which include epoxidation of two single-site double bonds and epoxidation of one two-sites double bonds, were obtained. The organic-phase reaction was found to be the rate-determining step. Thus, the organic-soluble methyltrioctylammonium chloride (Aliquat 336) was chosen as the phase transfer catalyst to enhance the reaction rate. The purpose of this work is to build up a rational reaction mechanism in which an active oxidation catalyst was synthesized from the reaction of hydrogen peroxide, sodium tungstate, phosphoric acid and quaternary ammonium salt. Based on the experimental data, a pseudo steady state hypothesis (PSSH) approach was considered for the variation of the concentration of the active oxidation catalyst during the reaction. The apparent rate constants of the organic-phase reactions were obtained. Factors which influenced the apparent rate constants were discussed in detail.