Cobalt oxide (Co3O4) nanocrystals have been synthesized successfully via a facile combustion method. The Li ions incorporated into the Co3O4 lattice should serve as a self-promoter for the crystallization, resulting in the drastic increase of particle size. The Li addition can complex the structure of the energy band gap. The optical absorption spectra indicate that the direct band gap of Co3O4 varied from 3.11 and 1.62 to 3.29-3.98 eV after introducing Li ions. This approach provides economically viable route for large-scale synthesis of this kind of nanomaterials. (c) 2007 Elsevier B.V. All rights reserved.