Optical and photoelectric spectral features of AgCd2GaS4 single crystal were explored. Optical band gap energy was estimated from the absorption and was varied within 2.18-2.28 eV (at ambient temperature) for the samples cut from different parts of the single-crystalline specimens. The results of the photoconductivity relaxation study within the temperature range 100-280 K were explored within a framework of the adhesion trapping level model. It was established that the AgCd2GaS4 crystals exhibit long-term relaxation of photoconductivity with adhesion levels at energies about 0.2 eV. (C) 2017 Elsevier B.V. All rights reserved.