This study investigated precipitation behavior and purification fraction of molybdenum according to the adding methods (batch and semi-batch) of α-Benzoinoxime in a simulated solution that was composed of 13 elements (Rb, Cs, Sr, Ba, Mo, Zr, Te, Ru, Y, Ce, Pr, Nd, Sm). Experiments were performed to dissolve precipitate without hydrogen peroxide that acts as a disturbing compound in a subsequent purification process. The precipitation fraction of molybdenum was similar irrespective of the adding method of α-Benzoinoxime. However, in the purification aspect, the addition of α-Benzoinoxime by semi-batch gave better results than by batch method. In 0.4 N NaOH solution without hydrogen peroxide, 97.5% molybdenum was dissolved from Mo precipitate within 5 minutes. This result was similar to the case of hydrogen peroxide addition, however, the addition only induced the rapid dissolution of α-Benzoinoxime re-precipitate. Besides, the dissolution method without hydrogen peroxide was favorable in the purification aspect because only small fractions of zirconium and ruthenium, 1.3 and 7.7%, respectively, were persent in the dissolving solution. Such a selective dissolution of molybdenum made possible to decrease roughly 50% of organic quantity of the dissolving solution to be fed in a subsequent silver coated activated carbon adsorption process.