The dissociation of aqueous trifluoromethanesulfonic acid (TFMSA) in the range 5-100 wt % has been studied by Raman spectroscopy and a values have been determined from integrated intensity of the band of the sulfonate group at 1035 cm"1 relative to that of the C-S stretching at 770 cm"1 taken as reference. Discrepancies are observed in comparison with previous IR estimates mainly at low acidities, and the possible reasons of the disagreement are discussed. The new results of TFMSA are compared with that of some other strong acids.