Yttria stabilized zirconia (YSZ) and zirconia (ZrO2) thin films without and with Nb-doping were prepared on Si substrate by rf-magnetron sputtering. Undoped YSZ and ZrO2 thin films had (001) orientation, and the orientation was unchanged by the Nb-doping. For both undoped YSZ and ZrO2 thin films, around 2.0 V ion-drift type hysteresis was clearly observed in capacitance-voltage (C-V) characteristics. Nb-doping into YSZ brought about the increase of lattice parameter up to 20 mol% of Nb, which suggests that Nb was incorporated into YSZ lattice up to 20 mol%. By the Nb-doping, the hysteresis in C-V characteristics for YSZ thin film was considerable decreased to around 0.1 V. Drastic suppression of the hysteresis in C-V characteristics was observed for Nb-doped ZrO2 thin film. In this case, the hysteresis was completely disappeared. These facts suggest that oxygen vacancies in YSZ and ZrO2 thin films would be suppressed or disappeared by Nb-doping. This means that Nb is a excellent dopant for both YSZ and ZrO2 to suppress the ion-drift type hysteresis.