Two tetragonal (t) zirconia-alumina composites were prepared by adding Al2O3 (20 vol%) into t-ZrO2 solid solutions doped with 3.0 mol% Y2O3, 1.6 mol% Nb2O5, 3.6 mol% CeO2 (Al20Ce) and 5.3 mol% Y2O3, 4.6 mol% Nb2O5 (Al20) as the femoral heads for the total hip replacements. The effect of machining and annealing on the hydrothermal stability and surface roughness of the composites was evaluated by comparing with the commercial 3 mol% Y2O3 stabilized t-ZrO2 (3Y-TZP). Machining was conducted by using the high-precision machine, where the spindle speeds (rpm 9000~18000) and the electroplated wheels (#400, 800) can be easily adjusted. The machined specimens were annealed at temperatures from 900 to 1300 oC and subsequently autoclaved for 5 days at 120oC under 0.3 MPa water vapor pressure. Although the phase stability and surface roughness of the machined composites were found to be inferior, the hydrothermal stability of the annealed and subsequently autoclaved composites was determined to be excellent as compared with that of the commercial 3Y-TZP. The lower phase stability of the machined composites was likely to be due to numerous machining damages (surface defects) of the composites than those of 3Y-TZP.