This paper deals with an original method for the preparation of ferrites with the garnet structure by coprecipitation. The different transformations of the coprecipitated hydroxide during heat treatment are studied and reported. YIG crystallization from amorphous oxide is significantly dependent of some parameters. However, pure homogeneous materials can be obtained at low temperature (800–850°C) for Al substituted YIG Y3AlxFe(5–x)O12 with 0.5<=x<=1.