Studies on the thermal decomposition behaviour of homogeneously precipitated Zr2(SO4)(OH)6 . 6H2O using a TG-DTA-MS coupling technique are reported for the first time. The positive ion mass spectra of evaporated gases during the process of thermal decomposition O+ (m/z 16); H2O+ (m/z 18); SO+ (m/z 48); SO2+ (m/z 64) versus temperature are also given.