Consolidated, monoclinic ZrO2 polycrystal was produced from undoped ZrO2 powders in air by flash sintering at the sintering temperature of 1350 degrees C for 5minutes or 3hours under an applied DC electric field of 175V/cm. When the ZrO2 was heated under the applied DC field, the electric current of the specimen steeply increased at the furnace temperature of 1335 degrees C below the sintering temperature of 1350 degrees C. When the furnace temperature was decreased from the sintering temperature of 1350 degrees C to room temperature, volumetric expansion associated with tetragonal-to-monoclinic phase transformation gradually took place at the furnace temperature from 1000 degrees C to 750 degrees C, and monoclinic ZrO2 body was remained consolidated even at room temperature in both specimens. In contrast, conventionally sintered ZrO2 without applying DC field exhibited the abrupt volumetric expansion at about 1000 degrees C, and shattered. SEM observation revealed the presence of grain-boundary second phase in the flash-sintered specimen for 3hours, which is a possible origin of keeping a bulk body at room temperature. The thinner second phase is considered to be formed also in the flash-sintered specimen for 5minutes, although the formation of the phase could not be observed clearly by SEM observation. On the other hand, XRD measurements showed that <001> directions of the monoclinic ZrO2 grains were oriented along the applied DC field after the isothermal flash sintering for 3hours while the grain alignment could not be observed in flash-sintered specimen for 5minutes. The alignment of ZrO2 grains observed in the isothermal flash sintering is considered to be closely related to the preferential direction of oxygen ionic conduction and the second phase formed along grain boundaries.