Amorphous arsenic trisulfide (As₂S₃) and arsenic triselenide (As₂S₃) are among widely investigated amorphous materials due to its interesting electrical, optical and photoelectrical properties. In order to improve the physical properties and recording characteristics, and to extend the spectral range of photosensibility, a special interest represents the mixed amorphous materials, like (As₂S₃):(As₂Se₃). Chalcogenide vitreous semiconductors (ChVS) of the As-S-Se system exhibit photostructural transformations with reversible and irreversible properties, and are promising materials as registration media for holography and optical information, for fabrication of diffractive elements, and other optoelectronic applications. Because many optoelectronic devices on amorphous semiconductors are based on the photoconductivity effect, special interests represent investigation of the stationary and non-stationary characteristics of photoconductivity. In this paper the experimental results of steady-state photoconductivity and holographic characteristics of amorphous (As₄S₃Se₃)_1-x:Sn_x thin films are presented. It was shown that the photoconductivity spectra depend on the polarity on the top illuminated electrode and on the Sn concentration in the host glass. The photosensitivity of amorphous ((As₄S₃Se₃)_1-x:Sn_x thin films is almost constant for all Sn-containing glasses. The Moss rule was used for determination of the optical forbidden gap E_g from the photoconductivity spectra. It was demonstrated that the investigated amorphous films are sensitive to the light irradiation and can be used as effective registration media for holographic information. The relaxation of photodarkening in amorphous (As₄S₃Se₃)_1-x:Sn_x thin films was investigated and was shown that the relaxation curves of transmittance T/T0 = f(t) can be described the stretch exponential function T(t)/T(0) = A0+Aexp[-(t-t0)/τ,]^(1-β). The kinetics of diffraction efficiency growth η(t) was measured by registration of the laser intensity of the 1-st interference maximum versus time exposure. With increasing of Sn concentration in amorphous (As₄S₃Se₃)_1-x:Sn_x thin films up to 6.0 at. % Sn, the diffraction efficiency η increases, than for higher concentrations of tin, decreases