The fabrication of phosphorus-based glasses containing Y 3 Fe 5 O 12 crystals by the incorporation method was studied. From transmission electron microscopy observation, there is only one rod-like crystalline phase identified as Y 3 Fe 5 O 12 existing in the glass matrix. When the content of YIG is 30wt.%, the as-cast sample shows a Faraday rotation of 85°/cm and a magnetization of 0.4emu/g in a field of 14kOe. After heat treatment, the magnetic and optical properties of the glass ceramic changed owing to the thermal diffusion of iron ions into the glass matrix.