a new rosin derivative—methylthiomethyl dehydroabietate has been synthesized from dehydroabietic acid and DMSO. The effects of reaction temperature, time, the amount of catalyst and mixing molar ratio of reactants on the yield have been investigated. The optimum reaction conditions were: the reactants were kept at 215 oC for 3h with dimethyl sulfoxide/ dehydroabietic acid mixing molar ratio of 22: 1 in the presence of 0.4% KOH catalyst ( based on the mass of dehydroabietic acid). The yield of product could reach 90%. The precise structure of the product was characterized as methylthiomethyl dehydroabietate by GC-MS, UV, FT-IR, High-Resolution Mass Spectrometry, 1HNMR and 13C NMR.