Reversible structural changes of As-rich As–Se nanolayers occurring during in situ thermal annealing and above-bandgap laser illumination were studied by synchrotron radiation photoelectron spectroscopy. It was found that the first thermal annealing of As₅₆Se₄₄ nanolayers led to a decrease of the concentration of As that can be connected with evaporation of more volatile As-rich fractions from the surface. This process is accompanied by structural rearrangements in the nanolayers. In situ green laser illumination of annealed samples causes an increase in the concentration of homopolar As–As bonds associated with As-Se₂As s.u., while the opposite effect was detected during further thermal treatment. These processes appeared to be reversible for three sequences of annealing and illumination. The observed effect of the reversible photoinduced structural modification is discussed in detail, and possible applications as an active optical medium for photonics are proposed.