To better understand the effect of inherent minerals in oil shale on the pyrolysis behavior of organic matter,Chinese Yilan oil shale is used as the raw material and its minerals are removed sequentially by stepwise acid treatment. The resulting samples are subjected to pyrolysis experiment on a thermogravimetric analyzer coupled with a mass spectrometer (TG-MS), and the effect of acid treatments on the organic matter structure is investigated by Fourier transform infrared (FTIR) and C-13 nuclear magnetic resonance (NMR). It is found that the acid treatments have little effect on the structure of organic matter, except oxidation of a tiny amount of aliphatic carbons to carboxyl by HNO3. Inherent calcite, iron oxide, and pyrite in the minerals, with contents of about 0.64, 2.63, and 0.60 wt %, respectively, have obvious catalytic effects on the decomposition of the organic matter. Acid treatment by HF + HCl increases the mass loss of organic matter during pyrolysis but decreases the formation of C2H4, C3H8, C4H10, C6H6, C7H8, and C6H6O. Quartz and kaolinite removed by HF + HCl treatment were reported to have little effect on the pyrolysis process; therefore, inherent montmorillonite may promote the reaction of organic volatiles to form coke and gas.