Boron carbide ceramics produced by spark sintering methods have more desirable mechanical properties than conventionally produced carbides. The boron carbide ceramics include amorphous boron, amorphous carbon, and Al2O3 powder as a sintering aid. The boron carbides may also contain a carbon nano fiber in a nearly homogeneously dispersed state. The sintered compact has a relative density of a boron carbide ceramic of approximately not less than 99%. The boron carbide ceramics are prepared preferably by subjecting a mixed powder of the starting raw materials and the carbon nano fiber to simultaneous synthesis and sintering using the spark plasma sintering method.