A theoretical analysis has been carried out to study the acoustic wave propagation through a hot planar gas-particle two-phase medium with emphasis on two-phase radiation effect. Extended from the earlier work, radiative absorption and scattering by particles as well as gas are considered and the relaxation model was used only to describe the temporal momentum interaction between gas and particles. The differential approximation for two-phase radiation was newly formulated. The present study showed that particle radiation alone without gas radiation was able to incur the radiation-induced wave attenuation. Moreover, once the gas radiation was involved, the wave attenuation due to radiation was apparently influenced by the particle as well as gas radiation. As the gas absorption coefficient increased, the additional wave attenuation appeared only when the gas absorption coefficient became larger than the given particle absorption coefficient. The radiative absorption by particles also affected the dispersion of wave. In addition, the wave attenuation in the low-frequency region disappeared as the scattering coefficient increased. It was also observed that the forward scattering augmented the wave attenuation in the low-frequency region for a fixed scattering coefficient while the backward one reduced it. Finally, in a higher medium temperature the wave attenuation by radiation was seen to be enhanced. (C) 2002 American Institute of Physics.