The mass spectrometer coupled with thermobalances (TG-MS technique) is commonly used for the identification of gases evolved during the heating of solid materials. The use of TG-MS for the quantitative determination of the composition of evolved gases is much rarer [1], but possible under specific experimental conditions. If the mass spectrometer is considered as a quantitative analytical tool, appropriate calibration is necessary. The TG-MS coupling enables the calibration of MS signal on mass changes observed by TG, but only if the mass decrease evaluated from TG is clearly related to one or several known gases. During the TG-MS measurement, only about one millionth of the furnace atmosphere is sampled for MS analysis. Thus, the sensitivity of MS detection (MS signal/gas amount ratio) is of great importance. Sensitivity is affected by the dynamics of gas evolution and their transport in the furnace atmosphere, which are influenced by the sample mass, heating rate, and the purge gas flow rate, especially. The effect of experimental conditions is discussed and demonstrated on the calcium oxalate decomposition, examples of successful use of this technique for the carbon surface analysis [2] and the decomposition of inorganic salts [3] are provided. Basic recommendations for improving the sensitivity of TG-MS measurements are summarized.