The technique of thermotherapy of tumors has been widely adopted in clinical treatments. But the efficiency is not so ideal in treating the tumor tissues growing in the depth of the body, because of the difficulties in transmission and concentration of heat energy.And another problem to be resolved in tumor thermotherapy is to measure the temperature of tumor tissues being treated with thermotherapy exactly and rapidly. The difficulties in thermo-dosage control affect the efficiency directly. The purpose of temperature autocontrol and stabilization in the thermotherapy of tumors can be achieved through Mn-Zn ferrite, a powdered magnetic absorber which absorbs electromagnetic wave and has Curic temperature. The efficiency can be improved by injecting Mn-Zn ferrite powder into blood vessesls in the course of thermotherapy.