Microstructure of cubic-ZrO2 (c-ZrO2) scale formed by oxidation of ZrC single crystals at 600 degrees C under an oxygen pressure of 2.6 kPa was observed by backscattered electron imaging in SEM and high resolution transmission electron microscopy equipped with EDX. The oxide scale was divided into two subscales, zones 1 and 2. It was revealed that an amorphous, carbon-rich phase 10 to 20 nm in width is formed near the interface between ZrC and zone 1 and that c-ZrO2 crystallites of 2 to 10 nm in size exist away from the interface in zone 1 while some growth of c-ZrO2 crystallites occurs in zone 2.