A comparison of the kinetic characteristics of MgCO3, CaMg(CO3), CaCO3, SrCO3 and BaCO3 decomposition in vacuum available in the literature, with the data calculated for three possible paths of the process has shown the one involving intermediate hydroxide formation to be most probable. This mechanism includes interaction of the carbonate with water vapor as the main, rate-limiting stage, followed by decomposition of the gaseous Ba hydroxide or condensing Mg, Ca and Sr hydroxides to the oxides and water. Some specific features of the process have been interpreted, in particular, the formation of a metastable calcium modification in decomposition of CaCO3 and CaMg(CO3)(2), as well as the anomalously high activation energies observed in non-isothermal decomposition of CaCO3 in the presence of CO2.