The change of mass of approximately 50 mg of the Ce2Sn2O7 powder sample used in this work was recorded upon heating under an oxygen flow up to 1000 Celsius. This method provides a direct and precise measurement of the oxygen stoichiometry according to the reaction Ce2Sn2O7+δ + (1 − δ)/2 O2 → 2 CeO2 + 2 SnO2. The theoretical mass gain for this reaction is 2.54% (δ = 0). Experimentally, we have measured a mass gain of 2.54% ± 0.02, which translates into δ = 0.00 ± 0.01. The residue of the sample after the thermogravimetric analysis was analysed by X-ray powder diffraction, corroborating the above chemical reaction.