Abstract: The adsorption isotherms of cholesterol from cyclohexane,ethyl alcohol and cyclohexaneethyl alcohol mixed solvent, and of egg-lecithin from ethyl alcohol and ethyl alcohol-water mixed solvent onto hydrophilic and hydrophobic silica gels have been determined (at 25℃).The contact angles On quartz and methylated quartz (with or without pre-adsorbed layers from above-mentioned solutions) have been determined. The results were explained in terms of the orientation of the adsorbed molecules and the surface properties of the SiO₂ and methylated SiO₂.