Graphite oxide (GO) was heated at 120 °C, 140 °C, 160 °C, 200 °C and 600 °C in ambient N₂ gas and the heated samples were investigated by X-ray diffraction, infrared (IR) spectroscopy, thermal gravimetry (TG), differential thermal analysis (DTA), elemental analysis and cation exchange capacity (CEC) tests. It was found that the interlayer distance decreases upon increasing the heating temperature up to 160 °C, and GO collapses to form graphite when heated at 200 °C and 600 °C. IR analyses showed that at 120 °C only water is lost, at 160 °C oxygen-containing groups (OCGs) decompose and at 200 °C or above almost all OCGs disappear except a few of the OH groups. TG/DTA analysis showed that a part of graphene sheets have been formed when GO is heated at 600 °C. CEC tests inferred that OCGs in GO are well preserved up to 140 °C, and the decomposition temperature of GO in this study is 140–160 °C, which is supported by the elemental analysis.