The pyrolysis of (MgCO3)3 . Mg(OH)2 . 3H2O was investigated using a combined TG-DTA-DTG technique in a flow of nitrogen gas. The TG-DTG curves showed three mass-loss steps corresponding to three endothermic peaks in the DTA curve, indicating the existence of (MgCO3)3 . Mg(OH)2, MgCO3 . 3MgO and MgO in the respective steps.