We report an oscillatory fluorescence decay of an electron donor-acceptor complex of hexamethylbenzene and tetracyanoethylene in CCl4 at room temperature, A fast spontaneous fluorescence decay with a characteristic time of 105 +/- 20 fs is observed, An underdamped oscillation of fluorescence is overlapped with this fast decay. The period of the oscillation is 209 +/- 4 fs, which corresponds to a frequency of 159 +/- 3 cm(-1) and is tentatively assigned to the intermolecular vibration in the excited state. The damping time of the oscillation is 280 +/- 30 fs.