Specular infrared reflectance spectra were made on hot pressed powder samples of rare earth sulfides of composition Ln2S3. The reflectance curve obtained from the Kramers-Kronig analysis is the deconvolution of the sum of the reflectance curves from the multiple grains, giving the bulk dielectric constant within the 25 cm−1 to 400 cm−1 range and transverse and longitudinal optic modes for the bulk material. Reflectance spectroscopy has shown to be a very good alternative to infrared transmission spectra in the far infrared range to obtain electro-optical information on ceramic powders.