In order to clarify the kinetics of the synergistic extraction of gallium with the mixed extractant of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) and 5-chloro-8-quinolinol, the initial extraction rate of gallium with the mixed extractant was measured using a stirred transfer cell. Based on the knowledge of the extraction mechanism of gallium with EHPNA or 5-chloro-8-quinolinol alone and the synergistic extraction equilibrium of gallium with the mixed extractant, the synergistic extraction mechanism of gallium with the mixed extractant of EHPNA and 5-chloro-8-quinolinol was clarified. The experimental data were well explained by the model presented in this article without any adjustable parameters.