The influence of the heart treatment and light exposure on optical and photoinduced properties of (As4S3Se3)1-x:Snx thin films are investigated. The thin films were characterized by X-Ray diffraction (XRD), and optical absorption spectroscopy. The XRD measurements showed that the Sn impurities in the (As4S3Se3)1-x:Snx essentially don’t change the shape of the FSDP of the X-ray diffraction patterns, the intensity and the position of the first sharp diffraction peak non-monotoniously depend on the Sn concentration. By the optical absorption spectroscopy the transmission spectra of bulk materials and thin films of (As4S3Se3)1-x:Snx (x=010 at.%) in the visible and near infrared regions have been studied. The modifications of optical parameters (optical band gap Egopt, absorption coefficient α, refractive index n) under light irradiation by halogen lamp of the amorphous thin films with different amount of Sn were measured and calculated. On the transmission spectra the red shift of the fundamental absorption edge under light exposure was observed, and the values of the optical band gap Egopt from the graphics in Tauc coordinates ( h )1/2=A(h - Eg) were obtained. The dispersion of the refractive index was examined. Moreover, manifestation of partial reversibility of the optical absorption after annealing was demonstrated. The relaxation of the relative optical transmission T/T0=f(t) under the light exposure ( =633 nm) for amorphous (As4S3Se3)1-x:Snx thin films also was investigated. The relaxation curves of photodarkening under light irradiation were processing using the stretched exponential presentation of the data: T(t)/T(0) = A0+Aexp[-(t-t0)/τ](1- ). Where t – is the exposure time, τ – is the apparent time constant, A – characterizes the exponent amplitude, t0 – and A0 – are the initial coordinates, and  - is the dispersion parameter (0<<1), and were estimated by a computer program.