The use of microwave heating has now been applied to a wide variety of industrial fields. Especially, the use of microwave energy for the firing process of the advanced ceramics has been reportedly found to offer significant advantages compared to the conventional thermal heating. Generally, in the volume production, we use the suscepor, which is the pyrogenetic substance to be heated the specimens externally and to play a very important role in firing ceramics. Recently, we found out that the powdered metal silicon compact is one of the good candidates as susceptor materials. However, its microwave heating mechanism has not been made clear, yet. Then, in this report, we carried out the fundamental studies about the heating behaviors of the powdered metal silicon compact mixed with aluminum oxide powder under the microwave irradiation at a frequency of 2.45GHz in a symmetrical single mode cavity TE01 and the analysis of products after heating by the X-ray diffraction method. From experimental results, it was found out that the attained temperature of the compact specimen under microwave irradiation was higher with increase of voltage along the voltage distribution in the single mode cavity. And it was also found out that the temperature was different with how to set up the compact specimen in the single mode cavity.