The thermal decomposition of calcium phthalate monohydrate, CaC~8H~4O~4.H~2O, was studied by thermogravimetric analysis and differential scanning calorimetry. The products of thermal decomposition at various tages were characterized by the powder X-ray diffraction, infrared spectrometry and gas chromatography-mass spectrometry. The radical reactions in the pyrolytic process were discussed. The thermal decomposition of CaC~8H~4O~4.H~2O proceeds in three stages: It was dehydrated at 160～260℃, pyrolyzed to form CaCO~3.C at 460~780℃ and CaO at 780~900℃. Pyrolysis of CaC~8H~4O~4 at 500℃ gave (C~6H~5)2CO and CO as the main volatile products, with a large amount of fluorenone, 9,10-anthraquinone, diphenylmethane, etc.

Key words: CALCIUM COMPOUDS, DIFFERENTIAL SCANNING CALORIMETRY, THERMAL DECOMPOSITION, O-BENZENEDICARBOXYLIC ACID, THERMOGRAVIMETRY