Thermal radiation dominates the heat transfer in an entrained bed type of coal or wastes gasification furnace operated in high temperature. This study is to evaluate the radiation properties of coal char or ash particles, which are necessary to predict the behavior of heat transfer of a multiphase flow in the furnace. The monochromatic extinction of the sample particles dispersed in carbon tetrachloride or KBr powder was measured spectroscopically under an atmospheric condition by using FT-IR. The spectra of extinction for any particle number density in a dispersion layer can be summarized in the form of the apparent extinction efficiency. The spectral extinction efficiency of fly ash was almost independent of the type of ash, but was influenced significantly by the carbon content in the char. The extinction efficiency measured was equivalent to the apparent extinction efficiency estimated by applying the refractive index from references in the past works into Mie's theory assuming a strong forward scattering of fly ash particles.