The paper presents a new, non-traditional method for the synthesis of barium metaniobate, BaNb2O6, and of a mixed barium-strontium metaniobate, Ba0.29Sr0.71Nb2O6, through the thermal decomposition of coprecipitation products. The conditions of quantitative precipitation of the metals as niobic acid and barium or barium-strontium oxalate were established. The mechanism of thermal decomposition of the coprecipitate was deduced from differential thermal analysis and X-ray diffraction date. Barium metaniobate forms at 470°C, below the temperature required in the synthesis based upon the solid-state reaction between Nb2O5 and BaCO3 (1100°C). The mixed barium-strontium compound is formed at 700°C, below the 1100°C used in the reaction between Nb2O5, BaCO3 and SrCO3.