Novel Ga-Sb-S chalcogenide glasses doped with Dy3 + ions are synthesized. Their thermal stability, optical property, structure and mid-infrared (MIR) emission property are studied. The glass thermal stability against crystallization is significantly improved by slightly adjusting the glass composition, and therefore the fibers with good optical quality are drawn. The Dy3 +-doped Ga-Sb-S glasses show good thermal stability, excellent infrared transparency, low phonon energy, and intense emissions around 2.95, 3.59, 4.17 and 4.40 μm. The substitution of a small amount of Sb with As reduces the crystallization tendency of the glass during the fiber drawing without making remarkable effects on the emission property. Spectral analyses indicate that the quantum efficiencies of the 2.95 mm and 4.17 mm emissions of Dy3 + ion in the Ga-Sb-S glass are 88.1% and 75.9%, respectively; and the respective stimulated emission cross sections are 1.1×10-20 cm2 and 0.38×10-20 cm2. The high quantum efficiencies and large stimulated emission cross sections of the MIR emissions in the Dy3 +- doped Ga-Sb-S glasses make them promising gain materials for the MIR lasers.