Our experimental study of the system AgAuS–AgAuSe was urged by the misfit in literature data on the isomorphism of sulfur and selenium in this series and on the existence of AgAuSe phase. Scanning electron microscopy, optical microscopy methods, electron microprobe analysis and X-ray powder diffraction method have been applied to study samples synthesized by heating stoichiometric mixtures of initial compositions AgAuS1–xSex (х = 0; 0.25; 0.5; 0.75; 0.875; 1).