Abstract: A number of X-ray patterns and electrical conductivities of five different samples of Ag-Cu-Se system have been measured. These samples of Ag-Cu-Se system: (Ag1.188, Cu0.812)Se, (Ag,Cu)Se; (Ag0.9, Cu1.1 )Se, (Ag0.8, Cu1.2)Se and (Ag0.6, Cu1.4)Se were prepared under controlled conditions. Analysis of the experimental data shows that Frenkel defects are predominated in (Ag1.188, Cu0.812)Se and Schottky defects prevailing in the other samples. The activation energy values △E calculated from the linear behaviour of electrical conductivity a with temperature (0-90℃) reveal that the impurity content increases in the direction of (Ag,Cu)Se→(Ag0.8,Cu1.2 )Se