Polycrystalline transparent magnesium aluminate "spinel" ceramics were fabricated by hot-pressing and hot isostatic pressing (HIPing) using commercially available MgO and Al2O3 Powders. Al2O3 content of spinet was systematically changed that can be expressed as MgO.nAl(2)O(3) with n = 1.0, 1.5 and 2.0. UV/visible and near-IR wavelength region light reflection and transmission behaviors of the spinet ceramics were quantitatively correlated to their microstructure to account for the optical quality of the fabricated materials. The stoichiometric spinet ceramic with n = 1.0 revealed a relatively poor optical transparency due to pronounced light scattering at the microcracked grain boundaries with a specular light transmission of similar to 20-40% in the visible wavelength range. On the other hand, Al2O3 rich compositions revealed a specular transmission of -40-60% in the same wavelength range with a high degree of transparency. Additionally, effect of chemical composition on the fracture toughness of spinet ceramics was investigated applying indentation and chevron notched specimen fracture toughness measurement techniques. The spinet ceramic with n = 2.0 revealed the highest fracture toughness with a mean value of similar to 2.02 MPa-m(1/2). Based on their optical and mechanical properties, potential of Al2O3 rich non-stoichiometric polycrystalline spinet ceramics for engineering applications requiring high optical transparency and improved fracture toughness was addressed.