The propagation of a sound wave in a polyatomic gas is studied by using the Hanson and Morse polyatomic gas model [Phys. Fluids10, 345 (1967)] in the Wang‐Chang and Uhlenbeck equation, with Maxwell’s diffuse boundary conditions. The model equation and the associated boundary conditions are transformed into a system of integral equations, which is then solved numerically. The computed results for attenuation and the speed of sound for nitrogen, oxygen, and air at 300°K, and a wide range of rarefaction parameters, are compared with the experimental data of Greenspan [J. Acoust. Soc. Am.31, 155 (1959)], and of Meyer and Sessler [Z. Phys.149, 151 (1957)], and previously reported theoretical results.