Abstract: Infrared absorption spectra of orange, black and transferred Sb2S3 samples have been Studied in the spectral range 200~4000cm-1. The pronounced difference between the different samples is the appearance of excess sulphur present in the orange and transferred samples except those of transferred at 543 K and the black Sb2S3. The change of sharpness of some IR peaks reveals the amorphous/crystalline change. The effect of the degree of crystallinity and stoichiometry on the energy gap values was investigated using optical method. The obtained dielectric parameters ε'and ε" of the different samples are thoroughly afFected by the degree of cryStallinity and smoothly affected by either the frequency or the temperature or both, except at lower frequencies.