The thermal decomposition of 2-(4-nitrophenyl)- and 2-(2,4-dinitrophenyl) malonic acids, the corresponding diethyl esters, and the respective sodium carboxylates has been examined using thermogravimetry. Thermal decomposition of the carboxylic acids occurs by sequential loss of two moles of carbon dioxide per mole of acid followed by volatilization of the nitroaromatic formed. The corresponding diethyl esters undergo rapid decomposition at temperatures approaching 200 degrees C to afford in addition to volatile products (carbon dioxide) significant amounts of nonvolatile residue.