Hydrogenation of 4-oxoisophorone has been studied over a 1% Pd/Al2O3 impregnated catalyst in supercritical CO2 (sc-CO2) medium at different reaction conditions. The effect of temperature, pressure, and reaction medium on the conversion and product selectivity is discussed. Phase behavior studies have also been carried out to determine the conditions at which a supercritical phase is formed as a function of various experimental parameters as well as the miscibility behavior of different reactant mixtures. A comparison of the sc-CO2 medium reaction with the conventional liquid-phase hydrogenation in organic solvents as well as CO2-organic cosolvents has also been made. The reaction rates in sc-CO2 medium are found to be comparable to that in commonly employed organic solvents. Selectivities different from liquid-phase reactions are observed under supercritical conditions. Catalyst deactivation is found to be much lower in sc-CO2 medium when compared to that in the organic solvent medium. The reaction mechanism leading to different products is discussed.