We studied the magnetic properties of ultrafine cadmium ferrite particles that had been prepared by the coprecipitation method and bulk material by the generally used ceramic method. The ultrafine particles showed ferromagnetic behavior, while the bulk material had no spontaneous magnetization. We evaluated a large anisotropy constant K (3.6×10 6 erg/cm 3) in the ultrafine cadmium ferrite particles. The enhanced magnetic nature of the ultrafine particles can be explained based on an idea of cluster formation which is relevant to cation distribution.