Nanostructured As-S-Sb-Te semiconductors were synthesized and characterized by X-ray fluorescence analyzer (XRF), X-ray diffraction, and optical absorption methods. The X-ray diffraction patterns of ivestigated powders show the presence of amorphous and nanocrystalline phases with the structural units As₂S₃, Sb₂S₃ and Sb₂Te₃. The transmission spectra in the region of wavenumbers ν = 1000 ÷ 6000 cm⁻¹ show a high transparence just with a single weak absorption band at ν = 2340 cm⁻¹ caused of the presence H₂S impurity. For the alloys of (As₂S₃)_x(Sb₂S₃)_1-x system, with increasing of the Sb₂S₃ trigonal structural units in the above mentioned system, the absorption edge is shifted toward lower photon energy, that corresponds to the optical band band gap about E_g. = 2.34 eV for As₂S₃, 2.1 eV for (As₂S₃)_0.65(Sb₂S₃)_0.35, 1.92 eV for (As₂S₃)_0.35(Sb₂S₃)_0.65 and 1.73 eV for Sb₂S₃.