The purpose of this work is to improve the epoxidation of a long-chain olefin. The conversion and yield from the epoxidation of 1,7-octadiene is greatly enhanced by using a new cocatalyst in the presence of hydrogen peroxide in an organic solvent/aqueous solution two-phase medium. An active intermediate of the catalyst [Q(3)PW(12)(O)(n)O-40, where Q = R4N] produced from the reaction of phosphotungstic acid (H3PW12O40), hydrogen peroxide, and Aliquat 336 is employed as the cocatalyst. The structure of the active intermediate of the catalyst was identified by instrumental analysis. A rational mechanism of epoxidation is proposed to account for the reaction from the experimental evidence. The organic-phase reactions, including two series reactions, are the rate-controlling steps to produce two products, viz., 1,2-epoxy-7-octene and 1,2,7,8-diepoxyoctane. The kinetics of epoxidation, including the characteristics of the catalysts and the effect of the amount of cocatalyst, agitation speed, quaternary ammonium salts, amount of Aliquat 336 catalysts, amount of hydrogen peroxide, amount of chloroform, pH value, organic solvents, and temperature on the conversion of 1,7-octadiene were investigated in detail. A kinetic model was built, from which a pseudo-first-order rate law is sufficient to describe the behavior of the reaction. The observed peculiar phenomena were also explained satisfactorily.