Fully densified TiO2 was obtained from spark plasma sintering (SPS) nanocrystalline rutile powder at a temperature of 720 degrees C. The TiO2 was densified under an applied pressure of 40 MPa at 720 degrees C. However, the applied pressure was not great enough to cause plastic deformation within the TiO2 nanoparticle compact. Therefore, simple plastic deformation by applied pressure could not lead to the abrupt densification of TiO2 during the SPS. In this work, the abrupt densification of nanocrystalline TiO2 was examined at a low temperature in terms of the Joule heat caused by the flow of current through the compact due to the reduction of Ti4+ to Ti3+.