Monolithic NbB2, NbB2-SiC, and NbB2-SiC-GNP samples were produced by spark plasma sintering (SPS), and the effects of additives on the mechanical and thermal properties, microstructures, and oxidation behavior of the samples were investigated. The addition of SiC up to 30 vol% decreased the Vickers hardness of the binary composites due to microcrack formation. The fracture toughness and oxidation resistance of NbB2 were improved with the incorporation of SiC. Fracture toughness was higher for all the composites in comparison to monolithic NbB2, moreover the highest value of similar to 5.2 MPa center dot m(1/2) exhibited by 3 vol% GNP-containing composite. A strong interface and homogeneous distribution of GNPs enhanced the thermal transfer properties and improved the oxidation resistance of selected NbB2-SiC ceramics in oxidation studies at 1200 degrees C. A combination of high mechanical properties, high thermal conductivity, and low mass gain was achieved for the NbB2-SiC-GNP samples with 1 and 3 vol% GNPs.