Monolithic zirconia materials (3Y-TZP, 10Ce-TZP, and 12Ce-TZP) and their composites with 30 vol% alumina were produced. Low-temperature aging degradation (LTAD) and mechanical properties of materials were investigated. For assessment of phase stability in the materials, aging experiments were performed in water at 90°C for 32, 64, and 128 days. The aging phenomenon was characterized and monitored using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Four-point bending was used to determine the flexural strength of materials before and after aging treatment in water at 90°C for 2, 4, and 6 months. The aging experiments resulted in different phase transformation rates for the materials studied. The 12Ce-TZP containing materials showed the highest resistance to low-temperature aging and 3Y-TZP containing materials showed the highest bending strength. When compared, no change in flexural strength was observed between the materials not exposed to aging and the aged materials.