This work focuses on the investigation of the stability of catalyst activity in the liquid phase methanol synthesis process. The effects of various kinds of metfhods to inhibit the deactivation of catalyst have been experimentally examined. The activity of catalyst was stabilized without lowering of activity by a suitable hydrothermal treatment, although the activity of the untreated catalyst decreased gradually with time. The additive and coating of hydrophobic material were effective for slowing down the crystallite size growth and inhibition of deactivation of catalyst. It was considered that hydrophobic material inhibited the adsorption of produced water onto the hydrophilic catalyst. Hydrophobic treatment of catalyst was found to be effective for liquid phase methanol synthesis from CO2 and H-2 using hydrophobic solvent.