Scanning electron microscope (SEM) observation combined with energy dispersive X-ray spectrometry (EDX) was applied to investigate Na+ ion dynamics at the grain boundary region in the Na4Zr2Si3O12 (NZS) sintered pellet. When electron beam of 200 pA illuminated a spot of 3 nm in diameter on the NZS sintered pellet for 100 s, a metallic sodium phase appeared. This new phase appeared to be liquid at 200 degrees C and crystalline with hexagonal habit at room temperature. When the specimen temperature was 300 degrees C or higher, this phenomenon was not observed because of the sodium vapour transpiration into the SEM’s vacuum column.