This study provides the evidence for hydrophobic hydration of CH3COOD as its aqueous solution was compressed by high pressure. On going from neat CH3COOD to diluted CH3COOD/D2O mixtures, the C-H vibration absorption bands do not reveal the solvent shift in frequency upon dilution, while the C-H absorption bands are altered into one prominent band at similar to2955 cm(-1) as the pressure was applied above 0.3 GPa. The possible explanation is the enhancement of C-H-O interactions between C-H and D2O under the condition of high pressure. Ab initio calculations predict that the CH3 stretching frequencies and intensities of acetic acid are hardly affected by the presence of water, if the methyl group does not participate in the complex formation. Nevertheless, the strongest absorption peak at similar to2928 cm(-1) is predicted in several low-energy (acetic acid)-(water)(x) complexes with the participation of C-H-O hydrogen bond. The reorganization of hydrogen-bond network or geometry is suggested to be responsible for the formation of C-H-O hydrogen bond.