In this paper, we prepared BaAl2O4 and Co:BaAl2O4 nanoparticles from aqueous solution of metal nitrates containing citric acid as a chelating agent by sol-gel method. The gel was heat-treated at temperatures ranging from 710°C to 1000°C. The heat-treated powders were characterized by X-ray diffraction analysis (XRD), infrared spectra (IR) and luminescence spectroscopy. From the results of the characterization, we find the prepared powders are pure nano-particles of BaAl2O4 after heat-treated at 900°C temperature. The emission spectra of Co: BaAl2O4 in the visible region indicates the existence of Co2+ in the tetrahedral sites of BaAl2O4 nano-crystal.