Experiments with a ballistic piston compressor were made to investigate certain thermodynamic properties of gaseous UF6. Measured gas pressures, volumes, and temperatures were analyzed with a computer program employing a numerical optimization scheme to arrive at the desired properties. The thermodynamic properties deduced include the UF6 constant volume specific heat, specific heat ratio, and the viscous coupling constant for UF6/He mixtures at temperatures up to 1500 K.