On the basis of the results of differential-thermal and X-ray phase analyses and measurements of the microhardness and emf of concentration chains in the range from 300 to 430 degree K, it is established that in the quasi-binary system Cu//2Se-Tl//2Se five compounds are formed - namely, CuTlSe, Cu//7Tl//3Se//5, Cu//3TlSe//2, Cu//8Tl//2Se//5, and Cu//9TlSe//5.