Ultrasonic absorption spectra have been measured in the frequency range from 40 kHz to 2 GHz for solutions of D-fructose in water and in two water-ethanol mixtures as well. It is found that a low frequency relaxation with relaxation time around 1 mus exists in the aqueous solution. The amplitude of that relaxation term is considerably smaller in the aqueous-ethanolic systems, in conformity with a reduction of the content of the alpha -D-fructopyranose tautomer. Our measurements confirm the assignment of the low frequency acoustical relaxation to a C-2(5) reversible arrow C-5(2) ring inversion of alpha -fructopyranose in solution.