The vibrational relaxation of the CO stretching mode of HCO2CH3 in CCl4 solution was measured using femtosecond infrared spectroscopy. Time-resolved spectra after excitation of the CO stretching mode revealed a new absorption other than that of the excited CO mode. Transient signals for the fundamental band and the absorption of the excited CO mode showed nonexponential kinetics having a subpicosecond component. A three-state kinetic scheme showed that the excited CO mode decayed via the v1 state of the CO mode. The subpicosecond decay component might be due to fast equilibration of the excited state with the adjacent 2nd excited state of the OCH3 stretching mode. Or it might be caused by solvent memory effects, which may cause unusually rapid nonexponential absorption decay. As demonstrated herein, time-resolved infrared spectra with high spectral resolution and sensitivity can provide detailed relaxation pathways of vibrational energy.