As 2(Se 1− x S x ) 3 glasses with x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared by direct quenching from the melt solution. The structure and stochiometry of the glasses were investigated by powder X-ray diffraction, Raman spectroscopy, and electron-probe-micro-analysis (EPMA) techniques. The photodarkening effect in the As 2(Se 1− x S x ) 3 glasses were observed under the influence of laser irradiations. The energy band gaps of whole series As 2(Se 1− x S x ) 3 glasses were examined by thermoreflectance (TR) as well as transmission measurements. Compositional dependences of the energy gaps of the glass system were evaluated. The relationship of the direct band gaps of As 2(Se 1− x S x ) 3 (0 ≤ x ≤ 1) glass is determined to be E g( x) = 1.52 + 0.28 x + 0.38 x 2 eV.