Magnesium aluminum spinel (MgAl2O4) transparent ceramics have excellent optical and mechanical properties, which have been widely used in bulletproof armor windows and high Mach fairing. To achieve densification of MgAl2O4 transparent ceramics, a relatively high sintering temperature is generally required. However, higher sintering temperature can lead to excessive grain growth of ceramics, which will affect its performance. Therefore, it is very significance for improving the performance and reducing costs of ceramics by introducing appropriate sintering aids to reduce its heat treatment temperature. In this article, the high-purity commercial MgAl2O4 powders were used as raw materials and La(OH)3 powders were used as sintering aids. The MgAl2O4 transparent ceramics were fabricated using vacuum sintering combined with hot isostatic pressing (HIP) post-treatment. The evolution of microstructure and phase composition were tested by XRD and SEM. The optical and mechanical properties of transparent ceramics were characterized using UV-Vis-NIR spectrophotometer and multifunctional mechanical material testing machine, respectively. The results indicate that La3+ effectively improves the densification rate of ceramics in the early and middle stages of sintering, and inhibits grain growth of ceramics in the later stages of sintering. After adding 0.01% (mass fraction) La2O3, the optical and mechanical properties of MgAl2O4 are excellent. The HIP sintering temperature required to achieve optimal optical quality is decreased from 1 650 ℃ to 1 600 ℃ and the corresponding average grain size is reduced from 7 μm to 3 μm.