Co 2+ -doped LiAl 5 O 8 (Co 2+ :LAO) nanocrystalline powder sample was obtained by sol–gel method. The gel with the composition of CoO–Li 2 O–Al 2 O 3 was prepared from lithium acetate, nitrates of aluminum and cobalt, citric acid, and was heat-treated at temperatures from 500 to 1000°C. The heated powder samples at different temperatures were characterized by differential thermal and thermogravimetric analysis (DTA/TG), X-ray diffraction analysis (XRD), transmission electron microscope (TEM), infrared spectra (IR) and absorption spectra. The results show that when the gel was heat-treated at 700°C, LiAl 5 O 8 nanocrystals with size of 20–40nm were formed. The absorption spectrum of the heat-treated powders is identical to that of tetrahedral Co 2+ ions, which shows that Co 2+ ions are embedded in the lattice sites of LiAl 5 O 8 nanocrystals and are coordinated with four oxygens.