There are many methods for measuring FT-IR spectra, for example, transmission, diffuse reflection, attenuated total reflection and so on. It is said that the transmission method is the most reliable method for qualitative and quantitative analysis of FT-IR spectra. The spectra of highly scattering samples such as coals or amorphous silicon powders measured by the transmission method, however, have large backgrounds with small relevant absorption peaks. Therefore, we investigated measuring methods for reducing the background itself. As a result, using a highly scattering 1R filter, we could clearly distinguish absorption peaks of amorphous silicon powders that were not found in IR spectrum measured by the normal transmission method. Our highly scattering filter is composed of fine Csl powders(<125*10−6m) and fine KBr powders(<125*10−6m).