Abstract: FT-IR spectra of oil shale and demineralized oil shale were studied by Lorentzian curve fitting and A-C factor, with the full-aliphatic-chain-bearing micritic paraffin taken as standard substance. The content and structure of various hydrocarbons in kerogen were analysed. The results showed that all the organic compounds in oil shale and demineralized oil shale were of the type-II kerogen. Demineralization enables the aliphatic branches to be stripped from the backbone of kerogen, but the overdemineralization is unallowable because it will make the aliphatic chain content in kerogen, the CH2/CH3 ratio and the ratio of aliphatic C-H to aromatic C-H all increase then decrease. The aliphatic chain content in the type-III kerogen is up to 54.06 %, while the values of CH2/CH3 ratio and the ratio of aliphatic C-H to aromatic C-H are 7.11 and 2.73, respectively. The removal of inorganic substance will improve the potential oil producibility of kerogen.