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 MgOY2O3 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 A0) by increasing the additive percentage from 0 to 5%, but it decreased (4.2195 A0) in 10% additive. Nanopowder was sintered by the SPS technique at 1400°C. MgO-2.5% sample had the highest relative density (99.1%) and transmittance (15%), with an average grain size of 0.41 μm. MgO-5% sample, however, had the highest hardness (10.57 GPa), thanks to the finer average grain size (0.25 μm).