Nanometer MgO was prepared via a sol-gel auto-combustion technique using magnesium nitrate as raw material and citric acid as chelating agent.IR spectra of the dried gel were used to investigate the structure of the precursors.By studying the different TG curves of magnesium citrate gel prepared by different methods,we found that a combustion process occurred and the nitrate ions acted as an oxidant in the combustion process.TEM photographs of synthesized powders from the sol-gel auto-combustion showed that the crystallites were uniform in size.In addition,the XRD pattern of this sample showed that the particle size was 8.9 nm.The BET curves,in turn,showed that the specific surface of the sample was 26.34 m2/g.The mechanism of the frothing process in restraining agglomeration is discussed.