Particulate composites composed of boride and carbide ceramics were found to have remarkably high hardness values. Two different compositions were produced by hot-pressing commercially available ZrB(2), SiC, and B(4)C powders. Using a Vickers' indentation load of 9.8 N, measured hardness was similar to 20 GPa for a ceramic containing 70 vol% ZrB(2), 15 vol% SiC, and 15 vol% B(4)C, but increased to similar to 29 GPa for a ceramic containing equal volume fractions of the three constituents. Hardness values also increased as indentation load decreased due to the indentation size effect. At an indentation load of 0.49 N, the hardness of the ceramic containing equal volume fractions of the three constituents was similar to 43 GPa, which was higher than the hardness values reported for so-called "superhard" ceramics at comparable indentation loads.