Amorphous arsenic trisulfide (As2S3) and arsenic triselenide (As2Se3) are widely investigated amorphous materials due to their interesting electrical, optical, and photoelectrical properties. Mixed amorphous materials, such as (As2S3):(As2Se3), are of special interest for improving the physical properties and recording characteristics and extending the spectral range of photosensibility. Chalcogenide vitreous semiconductors (ChVSs) 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, it is of particular interest to study the steady-state and transient characteristics of photoconductivity. In this paper, experimental results for steady-state photoconductivity and holographic characteristics of amorphous (As4S3Se3)1-x:Snx thin films are described. 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:Snx thin films is almost constant for all Sn-containing glasses. The Moss rule was used for determination of optical forbidden gap Eg from the photoconductivity spectra. It was demonstrated that the investigated amorphous films are sensitive to light irradiation and can be used as effective registration media for holographic information. The relaxation of photodarkening in amorphous (As4S3Se3)1-x:Snx thin films was investigated; it was shown that the relaxation curves of transmittance T/T0 = f(t) can be described by stretch exponential function T(t)/T(0) = A0 Aexp[-(t-t0)/τ](1-). The kinetics of diffraction efficiency growth (t) was measured by registration of the laser intensity of the 1st interference maximum versus time exposure. With an increase in the Sn concentration in amorphous (As4S3Se3)1-x:Snx thin films up to 6.0 at % Sn, diffraction efficiency  increases; at higher tin concentrations, it decreases.