Lanthanum-barium oxalate was prepared and characterised by chemical and thermal analysis, X-ray diffraction and plasma emission spectroscopy. X-ray analysis showed the presence of a uniphase system. The kinetics of decomposition of oxalates of La and Ba as well as coprecipitated La-Ba oxalate have been investigated in air using dynamic thermogravimetry. The decomposition of mixed oxalate occurred with two over-lapping exotherms, corresponding to the decomposition of lanthanum oxalate followed by that of barium. The kinetics of decomposition of the irradiated salt was studied over the same temperature range as that of the unirradiated one in air and activation energies obtained from the slopes of Coat-Redfern's plot. Kinetic analyses following various theoretical models of solid state reactions showed that the best fit was obtained for a third order reaction and geometrical models. It was evident that though there was increase in the activation energy as well as frequency factor with increasing radiation dose, reverse phenomenon takes place in the case of reaction rate. The effect of gamma -irradiation on the process and the mechanism involved therein has been discussed.