Monocrystals are synthesized and grown according to Bridgman-Stockbarger method, and the influence of rare earth elements (REE) as well as of γ-irradiation on electrophysical properties of (SnSe)_1-x - (SnSe)_x (Ln - Pr, Tb, Er) alloy system is investigated. During transition from SnSe to (SnSe)_1-x - (SnSe)_x solid solutions, a partial compensation of charge carriers occurs and additional scattering centres appear. At low temperatures T < 350 K after irradiation with γ-quanta, thermoemf in samples of p-type conduction becomes higher and decreases in those of n-type conduction. In addition, under the influence of γ-rays radiation, defects come into being causing a decrease in lattice heat conduction and a rise in electron heat conduction. REE impurities are supposed to be positioned among the points of crystal lattice during irradiation with γ-quanta and, moreover, Frenkel defects are formed.