Abstract: Mass spectra (MS) of cholesterol esters and halides were obtained by means of Electron Impact (EI), Field Desorption (FD) and Chemical Ionization (CI). The result shows that EI fragmentation process of cholesterol esters is determined mostly by the steroid nucleus, and there is almost no difference among the mass spectra of various compounds. FD-MS can supply both clear imformation of molecular weights of compounds and a fragment ion at m/e 369 due to the steriod nucleus. Besides having the same feafures as that of FD-MS, CI-MS of most compounds yield information of RGOOH structure. Therefore, mass spectra gained by these three ionization modes are satisfactorily used to analyse liquid crystals.