A phase diagram of the alloys of the ternary system of copper-germanium-tin was constructed on the basis of the data obtained by x-ray analysis. The isothermal section at room temperature was found to consist of eight single-phase regions (i.e. α,ζ,δ,ε1,ε,η′,Ge, and Sn), thirteen two-phase regions (i.e. α+ζ,α+δ,ζ+δ,ζ+ε1,ε1+δ,ε1+ε,δ+ε,ε1+Ge,ε1+η′,ε+η′,η′+Ge,η′+Sn,Ge + Sn), and six three-phase regions(i.e. α+ζ+δ,ζ+ε1+δ,ε1+δ+ε,ε1+ε+η′,ε1+η′+Ge,η′+Ge+Sn). No new phase was observed in these alloys of the ternary system.