Abstract: Maleopimaric acid can be synthesized by Diels-Alder reaction from rosin and maleic anhydride catalyzed by phosphato-molybdic acid. The effects of reaction parameters, such as catalytic amounts, temperature, times and rosin/maleic anhydride molar ratio, were investigated. Based on the experimental results, it is found that with mass part of catalyst 2.0%, toluene as solvent, reaction time 4 h and rosin/maleic anhydride molar ratio 1.7:1 the yield of 78.9% can be obtained.