High purity Al2O3 powder was used as raw material and MgO was used as additive to sinter alumina transparent ceramics in hydrogen atmosphere. EBSD image showed that, with the increase of the MgO content, the grain size decreased from 200μm (when no Mg was doped) to about 20μm (when the Mg doping amount was 1.0wt%), indicating that MgO had an inhibition effect on the grain growth. XRD analysis showed that the doping of MgO did not lead to the formation of new phases. A further refinement of cell parameters revealed that, when the doping amount reached 1.0wt%, lattice distortion occurred and the cell volume increased by about 80%, which was attributed to the formation and diffusion of oxygen vacancies. The Eg mode at ν=575cm-1 revealed by Laser Raman Spectroscopy suggested that AlO6 octahedra were distorted with the increase of the MgO content. And the frequency change of the A1g mode at ν=642cm-1 reflected the combined effect of ion mass and mechanical constant. Measurement of the optical transmittance indicated that, after the doping of MgO, a small amount of MgAl2O4 phase formed at the grain boundary, causing the transmittance to increase first and then decrease with the increase of the MgO content. And analysis of the dielectric properties showed that the change of the dielectric constant and loss with the frequency at room temperature resulted from ion relaxation polarization induced by the weakly bound ions in the AlO6 octahedron.