The crystallographic phase diagram for the Gd2O3-Fe2O3 and (Gd2O3 + Y2O3)-Fe2O3 system have been constructed by differential thermal analysis, quenching and X-ray diffraction. Single crystals of Gd3-xYxFe5O12 have been grown by the traveling-solvent floating-zone (TSFZ) method following the obtained phase diagram. It was found that the optimum growth conditions involved using a pre-melted rod and a growth rate of less than 0.5mm/h in oxygen atmosphere. (c) 2005 Elsevier B.V. All rights reserved.