The thermal behaviour of magnesium-n-alcoholates, branched magnesium alcoholates and magnesium diolates on the way to MgO was studied by IR-spectroscopy and thermal analysis. The covalent character of the Mg-O bond increases with increasing length of the alcoholates and diolates. The studied magnesium alcoholates and diolates decompose in air or oxygen atmosphere via alkoxy/hydroxy species. Thermal analysis shows that alcoholates and diolates decompose to MgO in a similar way; in the first TG-steps mostly hydrocarbon fragments are eliminated from the samples, the next TG-steps show mostly water and carbon dioxide as gaseous reaction products. The final decomposition temperature to MgO also increases with increasing length of the carbon chain of the alcoholates and diolates.