A theory is developed for the propagation of sound waves in a rigid, isotropic, and homogeneous porous medium filled with a compressible fluid, including both the effect of viscous dissipation and the effect of thermal comduction. With a capillaric model assumed, an expression for the permeability as a function of the frequency is also given. For very low frequencies (isothermal case) and very high frequencies (adiabatic case), the results reduce to those of a theory presented by Morse [J. Acoust. Soc. Amer.24, 696 (1952)]. The present theory can be used to determine the structural parameters of a porous system at a given frequency. Attenuation and phase factors are plotted as functions of a nondimensional frequency parameter for various combinations of the characteristic constants.