MgO nanopowders were synthesized through the co-precipitation method with different Y2O3 percentages (0, 2.5, 5, and 10 wt %). The nanocomposite powder was characterized by thermal gravimetric-differential thermal analysis (TG-DTG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and field-emission scanning electron microscope (FESEM) analysis. Y2O3 can have positive effect on synthesis and sintering of MgO-Y2O3 ceramic likewise particles size and densification process. Crystallite size decreased with increasing amount of Y2O3 additive, and it was 32.6 nm for MgO-10%, and the average particle size by FESEM image was 52.2 nm for this sample. Lattice parameter increased (from 4.2188 to 4.2243 A(0)) by increasing the additive percentage from 0 to 5%, but it decreased (4.2195 A(0)) in 10% additive. Nanopowder was sintered by the SPS technique at 1400 degrees C. MgO-25% sample had the highest relative density (99.1%) and transmittance (15%), with an average grain size of 0.41 mu m. MgO-5% sample, however, had the highest hardness (10.57 GPa), thanks to the finer average grain size (0.25 mu m).