Time-resolved transient grating spectroscopy has been applied to the study of the vibrational energy relaxation process in solution. The vibrationally hot azulene molecule in the ground state was produced by the photo-excitation of the S₁ ← S₀ electronic transition and the successive rapid internal conversion process. The vibrational energy dissipation process was detected by the propagation of the acoustic wave of the transient grating (TG) signal. By comparing the solvent temperature rise time determined by the TG method with the energy dissipation process of azulene determined by the transient absorption spectroscopy, the mechanism of the vibrational energy dissipation process was discussed. This spectroscopic method has been applied to the other molecules e.g., p-nitroaniline and N,N-dimethyl-p-nitroaniline, and solvated electron.