In order to better understand the mineralogical characterization of various density fractions of Longkou oil shale, float and sink tests were carried out to separate the raw oil shale samples into a series of fractions according to density, firstly. The mineralogical characterization of oil shale was investigated using the analytical methods of X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), and optical microscopy. Density distribution of Longkou oil shale indicated the ash content of oil shale with different density fractions increased with the increase of density fraction. The inorganic minerals composition of oil shale was mainly quartz, kaolinite, montmorillonite, calcite, analcime, dolomite, and pyrite. A comprehensive considering of the results of XRF, XRD, and optical microscopy of Longkou oil shale in each density fraction indicated there was a high content of kerogen in the low-density fraction of the oil shale. So beneficiation of kerogen from raw oil shale may be realized using the gravity separation method.