The change in the direction and flow rate of electroosmosis in capillary electrophoresis with the application of an external electric field has been demonstrated and measured by the current-monitoring method. Factors such as solution condition and capillary dimension affecting the direct control of electroosmosis have been measured and analyzed in detail with the proposed capacitor model. The capacitor model predicted reasonably well the trends of experimental results at various solution pHs, electrolyte concentrations, and capillary dimensions.