In₂S_3-xSe_x and (In₂S₃)_x(In₂O₃)_y thin films have been prepared on glass substrates using appropriate heat treatments of In evaporatedt hin films. X-ray analysis shows that In thin films which were annealed under sulfur atmosphere at 350°C were mainly formed by In₂S₃. A heat treatment o fthis binary in air at 400°C during one hour leads to (In₂S₃)_x(In₂O₃)_y ternary material which has a tetragonal structure with a preferred orientation of the crystallites along the (109) direction. Similarly, a heat treatment of In₂S₃
in selenium atmosphere at 350°C during six hours leads to a new In₂S_3-xSe_x ternary material having tetragonal body centered structure with a preferred orientation of the crystallites along the (109) direction.Optical band gap,refractive index and extinction coefficient values of In₂S_3-xSe_x and (In₂S₃)_x(In₂O₃)_y thin films have been reached. Moreover, correlations between optical conductivity, XRD, AFM and Urbach energy of such ternary thin films have been discussed. Finally, the recorded formation disparity between the quaternary (In₂S₃)_x(In₂O₃)_y and ternary In₂S_3-xSe_x compounds has been discussed in terms of the Simha–Somcynsky and Lattice Compatibility theories.