The subsolidus phase relations of the Eu 2 O 3 +SrO+CuO ternary system have been investigated by X-ray powder di4raction. All samples were synthesized in air at 950+10003C. The system can be divided into nine three-phase regions and four two-phase regions. In this system, there exist two solid solutions, Sr 14+x Eu x Cu 24 O y and Eu 1؉x Sr 2؊x Cu 2 O y , and one ternary compound, Eu 0.8 Sr 1.2 CuO 3.4 . The solid solution Sr 14+x Eu x Cu 24 O y (04x46) crystallizes in an orthorhombic unit cell with space group Fmmm and lattice constants of a ؍ 3.950+3.981 A > , b ؍ 11.475+11.298 A > , and c ؍ 13.401+12.827 A > . The solid solution Eu 1؉x Sr 2؊x Cu 2 O y (04x40.4) belongs to an orthorhombic system with space group Immm and cell parameters a ؍ 3.761+3.775 A > , b ؍ 11.385+11.252 A > , and c ؍ 20.019+ 20.069 A > . The ternary compound Eu 0.8 Sr 1.2 CuO 3.4 crystallizes in an orthorhombic unit cell with space group Immm and lattice constants of a ؍ 3.713 A > , b ؍ 3.787 A > , and c ؍ 12.636 A > . A comparison of the Eu system with reported systems of La, Nd, Ho, and Y indicate that the phase diagrams become complicated with an increase in the lanthanide ion size.