Sound absorption and velocity have been measured at 65 Mc/sec in aqueous sulfuric acid solutions at concentrations up to 13% oleum. The absorption goes through peaks at mole fractions of 0.5 and 1.0; the adiabatic compressibility has been calculated, and goes through a valley and a peak, respectively, at these two concentrations. No relaxation is observed. This behavior is discussed, but it has not been possible to distinguish very definitely between “structural” and “chemical” absorptions.