This paper explores the effects of dopant content on the aging behavior of tetragonal zirconia polycrystal (TZP). TZP powders with varying Y2O3 content (1.75-3mol%) were synthesized by co-precipitation. After the green body of as-prepared TZP powders being isostatically pressed at 200 MPa and sintered at 14000C for 3 h in air, a range of TZP ceramics were fabricated. As-synthesized TZP ceramics annealed at relatively low temperatures with the presence of water or water vapor. XRD analysis was conducted for phase identification and determined a tetragonal to monoclinic transformation. Microscope imaging displayed the changes of aged TZP surface structure. It is believed that the degradation of TZP might be caused by the reaction between Y2O3 and H2O. The mechanism of low temperature degradation of TZP was discussed.