The purpose of this study is to investigate the thermal characteristics of Mg1-XCaXFe2O4 ferrite powder by applying AC magnetic field and to predict the effect of thermal coagulation in vivo. We found that heating characteristics of the ferrite powder became greater as the frequency through the 400 kHz to 700 kHz range. The highest heat generation was attained using 7-15 nm ferrite powder. We also carried out a heat transfer simulation in which we were able to demonstrate that this material has sufficient heat generating characteristics to thermally coagulate a tumor cell and that it is possible to predict the range of the coagulation from the present simulation. (c) 2006 Springer Science + Business Media, Inc.