Direct investigation of the changes of functional groups of organic matter in oil shale during the pyrolysis is important for understanding its thermal conversion for shale oil generation. In this paper, an in situ Fourier transform infrared (FTIR) analyzer with a heater was used to study the pyrolysis of Huadian oil shale and its demineralization samples (kerogen concentrates) during the heating up to 600 degrees C. Transition state theory (TST) was used to analyze the conversion mechanisms of different oxygen-containing functional groups to H2O, CH4, CO, etc. The pyrolysis of dried oil shale begins with the rupture of C-OH and subsequently progresses to the decomposition of thermosensitive oxygen-containing groups (C-O and C=O in sequences). Also, then, aliphatic compounds will begin to decrease obviously from 350 degrees C due to cracking and evaporation while aromatic compounds exhibit excellent thermostability. The minerals in oil shale produce catalytic effects on the conversion of kerogen to bitumen, making the pyrolysis reactions easier in oil shale than in pure kerogen.