The mechanical milling method was used in this study to investigate the effect of adding Cr2O3, ZrO2, and Nb2O5 on the sintering behavior and microscopic structure of alumina ceramics. To this end, alumina powder was used as raw material and Cr2O3, ZrO2, and Nb2O5 powders as additives in weight proportions of approximately 0.6%, 10%, and 1 wt% respectively. Composite powders were pressurized at 300 MPa inside a metallic forming mold. The samples were then sintered at 1300 to 1500ºC for 2 hours in the furnace. The x-ray diffraction method was used for identifying the resulting phases and a scanning electro-microscope (SEM) for examining the resulting microstructures. The results showed that adding the above oxides caused an increase in the density and hardness of the sintered sample, which reached their respective maxima at 1500°C. The greatest density and hardness were obtained for the alumina-Nb2O5 sample as 3.78 g/cm3 and 1292 HV respectively. On the other hand, the grain size of the matrix in the alumina sample increased after the process of sintering in the presence of the above oxides was completed, reaching a maximum value of 3.68 mμ.