FTIR spectroscopy was used to study the hydrogen bonding of benzoic acid and salicylic acid with ethanol and methanol in supercritical CO2. The extent of hydrogen bonding was estimated from the hydrogen-bonded and nonhydrogen-bonded infrared absorption bands. It was found that the solutes and the cosolvents can form hydrogen bondings even their concentrations are very low. At constant solute concentrations, the extent of hydrogen bonding increases with cosolvent concentrations.