Excitation and fluorescence spectra of the 3400-Å system of S 2O are reported for the first time at low resolution. Fluorescence quantum yields for the upper vibronic states are measured as a function of absorption peaks (bands). Because of the unusually small quantum yields of some absorption peaks and because of the broader bandwidths of some fluorescence bands, multiple transitions are assumed to occur within each "single" absorption peak. Thirty-one fluorescence peaks are identified and grouped into five v″ 2 progressions. Although v″ 2 up to 8 was assigned, no new vibrational constants are derived because of the low spectral resolution.