Sound waves can be used for measurement of thermophysical properties for fluids. The author developed apparatuses for acoustic resonance measurement with a spherical and a cylindrical cavity to measure thermophysical properties of gas samples. In the spherical cavity, acoustic resonance frequencies can be accurately measured so that speed-of-sound of gas samples can be also accurately determined. Speed-of-sound is one of the thermodynamic properties related to density and compressibility, and is useful information to develop the thermodynamic equations of state for fluids. Recently, the author measured speed-of-sound for refrigerants with very low global warming potential, contributing to the development of the equations of state for them which are required to evaluate the cycle performance of the air-conditioning system. On the other hand, the half-width of acoustic resonances can be accurately measured using the cylindrical cavity, leading to obtain viscosity and thermal conductivity of gas samples. In the future, the author plans to accurately measure speed-of-sound of mono-atomic gas samples to derive the thermodynamic temperature, and reevaluate the international temperature scale (ITS-90).