Thermal bitumen is an important intermediate derived from kerogen decomposition during oil shale pyrolysis. In this study, free bitumen (FB) and bound bitumen (BB) were obtained by extracting oil shale chars (300- 550 °C) before and after demineralization, and then analyzed by liquid chromatography fractionation, Fourier transform infrared spectroscopy, and gas chromatography/mass spectrometry. The FB yield first increased and then decreased with increasing temperature, and the maximum value was 2.10% at 400 °C. The decarboxylation of acids and decomposition of esters at 350-450 °C decreased the content of these compounds. Meanwhile, the intense cracking reactions of aliphatic compounds and alkyl chains at 400-450 °C decreased the carbon chain lengths and molecular weights of these compounds. From the analytical results obtained for the BB fractions, we suggest that some carboxylic acids or carboxyl group-containing compounds may be trapped on carbonate particles by the formation of Ca2+COO- bonds, whereas other oxygenated compounds (e.g., esters and phenols) can be adsorbed preferentially by clay minerals through Lewis acid-base interactions.