The results of experimental investigation of the fundamental optical absorptionOptical absorption edgeAbsorption edge of glassy thin filmsThin films of the AsS3-GeS4 system are presented and discussed. The films were grown via thermal vacuum evaporation of powder of relevant glasses onto optical quartz substrates. The study was focused on the optical measurements to reveal the character and spectral position of the absorption edgeAbsorption edge, as well as to the effect of both glass composition and annealingAnnealing on optical forbidden gaps and characteristic energies (Δ) of glasses in question. The absorption edgeAbsorption edge was found to concur with usual behavior established for disordered materials: at high photon energy hv > Eg, it is described by a parabolic function but at low energy hv < Eg by an exponential lawUrbach tail (Urbach tail). The quadratic part of the absorption edgeAbsorption edge allowed to determine the optical forbidden gap Eg. It is shown that the glass composition and the thermal treatment influence the spectral position and slope of both parts of the absorption edgeAbsorption edge, but they especially strongly affect the slope of the exponential tail. The results are explained in terms of topological transformations due to glass composition change and structural self-organizationSelf-organization, as well as their effect on concentration and energetic distribution of localized states inside of the forbidden gap.