The room temperature section of the phase diagram of Co-Ge-Sn ternary system has been determined by means of X-raypowder diffraction method.The section determined consists of 12 single-phases,22 two-phase regions,and 11 three-phase re-gions.Two new phases,called δ and η respectively in this paper,have been found.The former is a binary phase with invariablecomposition(80.46at%Sn)corresponding to formula CoSn,and the latter is a ternary phase occuping a homogenous range.Theexperimental data also show that CoGe phase has a smaller region than that in Ref.1,2,while β-Sn,Ge,CoSn,CoSnandCoGeare phases with invariable compositions.