The synthesis of barium metastannate, BaSnO₃, by heating mixtures of metal oxalates, either physically mixed or subjected to a phase of mechanical activation, up to temperatures in the range 750- 1200 °C has been studied. Simultaneous thermogravimetric-differential scanning calorimetric (TGDSC) analyses and powder X-ray diffractometry have been applied to check the advancement of the reactions. BaSnO3, though slightly contaminated by BaCO₃, can be obtained by heating the activated mixture up to T ≥ 1000 °C while heating a sample of a physical mixture at temperature as high as 1200 °C resulted in a mixture of BaSnO₃, SnO₂ and Ba₂SnO₄. The heat capacities of BaSnO₃ samples prepared at temperatures between 1000 and 1200 °C have been measured by modulated temperature differential scanning calorimetry (MTDSC) in the temperature range 50-400 °C.