The thermal behaviour of anhydrous CaBr2 in N2 and O2 atmospheres containing H2O was investigated with the method of simultaneous TG, DTG, DTA and EGA (derivatograph). A method for the continuous determination of the amounts of Br2 and HBr evolved from the heated sample was elaborated in the presence of each other, and the course of the gas evolution was followed. It was found that water vapour does not react with CaBr2 in either a N2 or an O2 atmosphere, and no HBr is liberated. Under the given conditions CaBr2 completely decomposed in an O2 atmosphere between 500 and 1000°, with the formation of CaO and Br2, while in a N2 atmosphere between 700 and 1000° the material lost about 3 % of its original weight, due to evaporation.