The effects of 0-5 wt% Al2O3 addition on the aging sensibility and strength degradation of 3-mol-yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) were studied in this study. X-ray diffraction and field emission scanning electron microscopy were used to study the microstructures of aged specimens. The results showed that a small amount of Al2O3 addition could effectively improve the aging resistance of 3Y-TZP. The evolution of mechanical properties with aging time is different for 3Y-TZP with and without Al2O3 addition. Compared to the flexural strength, the fracture toughness and Vickers hardness of specimen are more susceptible to aging. The grain boundary segregated Al3+ plays a key role in retarding the tetragonal-to-monoclinic phase transformation of 3Y-TZP during aging.