The boundaries of glass-forming regions in the Sm2S3–Ga2S3–EuS system have been located using simultaneous thermal analysis, X-ray diffraction, and X-ray microanalysis. We have studied IR spectra of glass with the composition (Ga2S3)0.80(Sm2S3)0.10(EuS)0.10 and its stability in an inert atmosphere. The glass has been shown to soften at 985 K (Tg), which is accompanied by an endothermic peak. It crystallizes at 1112 K (Tx). Exothermic peaks observed in the range 1203–1222 K suggest that this glass has a tendency to decompose in several steps. In the IR spectra of the glasses, the bands due to the M–S (M = Sm, Ga, Eu) bonds have higher intensity and are shifted to higher frequencies relative to those in the spectra of their crystalline constituent components, which is probably due to the increase in M–S bond covalence.