Ultrafine MgAl2O4 powders have been successfully synthesized by solid-state reaction from the mixture of AlOOH and MgO at the lower temperature. The samples were investigated by DTA/TG、XRD and SEM analyses. The results showed that AlOOH can be decomposed into γ-Al2O3 from DG/TDA curves, which can improve the activity of Al2O3 and promote the process of solid-state reaction. The XRD analysis showed the single-phase MgAl2O4 was formed at 1400°C. Meanwhile it was detected by ICP-MS that the purity of powders was 99.995%. The SEM images showed that the mineralizer containing fluoride such as AlF3, NH4F can promote the resultant to grow into regular octahedrons and disperse the particles. The XRD analysis indicated the mixture containing 5% AlF3 can transform the integrated MgAl2O4 powders at 1200°C, nearly 200°C lower than general solid-state reaction. Furthermore, The SEM images showed that fluoride can crystal the fine particles into the larger MgAl2O4 crystals, about 0.5～1.5µm.