Boron Carbide is an attractive material for various applications that require high hardness and neutron absorption. Fully dense boron carbide bodies are usually fabricated using hot pressing at temperatures above 2000 °C. Therefore, the production cost is very high, that constitutes the major drawback for widespread applications in the fields of defense and nuclear energy. An alternative route to decrease the production costs is the reaction-bonded technique (RBBC). In this latter, a preform of porous B4C is obtained by compaction and partial densification. Then the material is infiltrated by molten metal or alloy. The metal can react with residual carbon and boron carbide to form carbide. This technique was extensively studied using conventional furnace but the use of microwave as a source of heating, as not used for this purpose so far, or only in a very few attempts. In the present study, the microstructure and mechanical properties of reaction bonding B4C infiltrated by silicon using microwave (2.45GHz) heating will be presented. The results will be discussed in the light of conventional RBBC.