Abstract: Maleic rosin acid was prepared using rosin and maleic anhydride as raw materials. Effects of different reaction conditions on the reaction were investigated by single factor experimentation, and the optimum conditions were found to be as follows: mole ratio of maleic anhydride to rosin 1.1∶1, reaction temperature 190 ℃, reaction time 4 h. The structure of maleopimaric acid anhydride was characterized by IR and single crystal X-ray diffraction. It was found that the configuration of maleopimaric acid anhydride was the classical type of diterpene compounds. The prepared maleic rosin was hydrolyzed and purified by potassium salt method to obtain maleic rosin acid with purity of 95.3% and yield of 81.5%. The structure of maleic rosin acid was verified by means of IR, 1H NMR, 13C NMR and MS.