Zinc oxide powders carbonated at 8 and 13 degrees C in an atmosphere of carbon dioxide (1 atm) and saturated water vapor were investigated by X-ray diffraction analysis and TG/DTA. Similar results were obtained for carbonation at both temperatures. Multiple phases coexisted. The predominant phase changed approximately from the oxide to the normal carbonate via a basic carbonate, as reported by Ohkuma et al. (Nihon Kagaku Kaishi, (1987) 802). Endothermic weight loss was observed at similar to 90, 220-250 and 340 degrees C. A tentative formula was proposed for the basic carbonate; Zn3CO3(OH)(4) . 2H(2)O. Decomposition reactions were proposed for the first and second endothermic weight losses, Zn3CO3(OH)(4) . 2H(2)O --> Zn3CO3(OH)(4) + 2H(2)O up arrow and Zn3CO3(OH)(4) --> 3ZnO + CO2 up arrow + 2H(2)O up arrow, respectively. The third endothermic weight loss was attributed to the decomposition of the normal carbonate.