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The subsolidus phase relations of the Eu2O3-SrO-CuO ternary system have been investigated by X-ray powder diffraction, All samples were synthesized in air at 950-1000 degreesC, The system can be divided into nine three-phase regions and four two-phase regions. In this system, there ex;ist two solid solutions, Sr14-xEuxCu24Oy and Eu1+xSr2-xCu2Oy, and one ternary compound, Eu0.8Sr1.2CuO3.4. The solid solution Sr14-xEuxCu24Oy (9 less than or equal to x less than or equal to 6) crystallizes in an orthorhombic unit cell with space group Fmmm and lattice constants of a = 3.950-3.981 Angstrom, b = 11.475-11.298 Angstrom, and c = 13.401-12.827 Angstrom, The solid solution Eu1+xSr2-xCu2Oy. (0 less than or equal to x less than or equal to 0.4) belongs to an orthorhombic system with space group Immm and cell parameters a = 3.761-3.775 Angstrom, b = 11.385-11.252 Angstrom, and c = 20.019- 20.069 Angstrom. The ternary compound Eu0.8Sr1.2CuO3.4 crystallizes in an orthorhombic unit cell with space group Immm and lattice constants of a = 3.713 Angstrom, b = 3.787 Angstrom, and c = 12.636 Angstrom. 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. (C) 2001 Academic Press.