Abstract: The methylated silica gel has been produced by the reaction between the surface silanql groups and ClSi(CH₃)₃vapor. The adsorption isotherms of acetic acid from carbon tetrachloride onto silica gel and methylated silica gel heated at various temperatures have been determined at 25℃, and the above mentioned silica gels have been studied by TGand IR. The results indicate:(1) the adsorption of acetic acid from carbon tetrachloride onto methylated silica gel decreased greatly, probably due to the concentration of the free hydroxyl groups for methylated silica gel decreased greatly as the IRshows, (2) As the surface methyl groups were destroyed at 500℃, the adsorption ability was restored when the methylated silica gel treated at>500℃; (3) after the methylated silica gel treated at high temperature, the adsorption ability was restored owing to that the surface free hydroxyl groups were reproduced.