The phonon dispersion curves of C-centred monoclinic beta gallium at its melting temperature, 256.8K, have been determined by the neutron inelastic scattering technique, using three-axis spectrometers at the Institut Laue-Langevin high-flux reactor in Grenoble. Measurements were made in the Xi x (and Sx), Delta , Xi z, Sz and R directions. In view of the metastable character of beta Ga, the sample crystal was grown and oriented in situ. The most unusual feature of the dispersion curve occurs in the Xi x (Sx) or ( xi 00) direction, where the acoustic mode polarised along the propagation direction peaks in frequency at xi approximately=0.5, and then falls to a very low frequency at xi =1. This behaviour suggests a desire to double the unit cell by suppression of the C-centred lattice points, but no such doubling has actually been observed.