The capsules containing magnetite has been used in several applications. Conventional methods for preparing capsules containing magnetite have not achieved a high rate of magnetite content. In this research, we succeeded in preparing capsules containing a high proportion of magnetite with a new method that uses a magnetic field. These capsules are prepared by interfacial polymerization of polyamide. The capsule size is controllable in the approximate range of 20-1000 mum. The method can possibly be used for even smaller capsules with improvement of apparatus. Calculation of density showed that the capsules contained magnetite at a rate of 50% or more. They are believed to be easily mass-produced and their industrial application is expected.