YIG precursor particles were synthesized by homogeneous precipitation via the thermal decomposition of urea in metal chloride salt solution. The precursor particles formed consisted of yttrium hydroxyl carbonate containing some hydrate and chloride ions together with iron oxyhydroxide. Even though the obvious exotherm and endotherm reactions did not appear in the thermal analysis of the precursor particles thermal decomposition of the particles was proceeded by continuous reaction of step-wise stage ; dehydratrion phase transition of iron oxyhydroxide to oxide. With increasing the heat-treatment temperature. YIG crystalli-zation proceeded by solid state reaction between intermediate YFeO3 and Fe2O3 above at 85$0^{circ}C$