Fully transparent polycrystalline spinel(MgAl2O4)has been prepared by combined vacuum sintering and hot isostatic pressing. This paper investigated transparent polycrystalline spinel optical properties sintered in different atmospheres and discussed the effect of sintered processing parameters on the development of the microstructure and transmission properties. The optical transmittance of the specimen sintered at 1500°C following HIPed at 1800°C was nearly the same as that of single crystal spinel. The transmission properties of spinel can be improved with the increase of temperature and pressure of sintered/HIPed spinel. Specimens sintered in vacuum following HIP have higher transmittance than those sintered in air or in hydrogen.