Sodium deposition in β-, β"-Al2O3 and Nasicon (Na3Zr2Si2PO12) was studied by using EPMA. Based on the mechanism of ion transportation and electrolytic deposition with a diminished carrier concentration, a kinetic equation for sodium deposition has been derived, which can fit well the time dependence of the sodium counts during electron bombardment. Since an abundant source of mobile Na+ ions exists in the large single crystal, the rise of the curve of beta-Al2O3 extends over a long period of time. However, the crystallites in the Nasicon polycrystal are small (+ ion therefore may be provided insufficiently at the electron bombarded point for a prolonged deposition due to the hindrance of the grain boundaries in the ion transport process. The deposition attains its saturation limit rapidly.