Polycrystalline magnesium aluminate spinel is a promising transparent ceramic for several applications like for example effective armor applications. This spinel can be elaborated by conventional multi-stage processes such as pressureless sintering followed by hot isostatic pressing. Nevertheless, one step spark plasma sintering is an approach less time-consuming. It has been confirmed that the application of pressure simultaneously with the sintering allowed for the fabrication of fine-grained and fully densed ceramics optically transparent. In this work, high-density bulk MgAl2O4 was fabricated from a nanopowder by high pressure spark plasma sintering (SPS) technique. A measure of Real In Line Transmission has been performed to evaluated the transparency level of samples. It is shown that by applying high pressure (76MPa to 1,5GPa), densification starts at lower temperature and are accelerated, the microstructure is finer. With the increase of the applied pressure, compacity of green pellets is strongly increased. This can be easily explained by an important modification of the granular arrangement with first an inter-agglomerate reorganization then an intra agglomerated arrangement and finally and superplastic deformation of nanoparticules. TEM analysis on green compact and sintered samples allowed to observed the constraint level of grains and the evolution of crystallite domains with the increase of pressure. Densification activation energy has been calculated to show the impact of pressure during sintering thermal treatment.