Brillouin spectra in molten Antimony Trichloride are investigated for the first time. Measurements are performed both in the normal and in the supercooled region. The acoustic velocity and absorption, obtained by a refined method of analysis of the experimental data, as function of frequency and temperature, show a dispersion that is characteristic of associated liquids. This acoustic anomaly is interpreted in terms of a relaxation phenomenon in which the strong intermolecular forces are involved.