Sound attenuation and dispersion by small, dense particles suspended in a gas are studied analytically and experimentally. A theory for attenuation and dispersion based on particulate relaxation processes is given. The close relationship between particulate relaxation and relaxation mechanisms due to lagging molecular or atomic internal degrees of freedom is displayed. The particulate relaxation theory predicts attenuation and dispersion, in close agreement with existing, more‐detailed theories in the vicinity of ωτd=1, where the attenuation per unit wavelength is a maximum (ω is the circular frequency, τdis the dynamic relaxation time of the particles). The experimental study consists of measurements of attenuation and dispersion in an acoustic interferometer. The interference tube is filled with an aerosol composed of oleic acid particles in nitrogen. Particle size and concentration are measuredin situby spectrophotometric tests. Dispersion measurements, taken at low values of ωτdwhere no previous measurements have been made, indicate good agreement with the theory. Attenuation measurements taken in the range of ωτdfrom 0.1 to 4.0 show good agreement with the theory. In particular, they confirm the existence of the predicted maximum. [Work supported by the Power Branch of the U. S. Office of Naval Research.]