Abstract Several cermets with nano-TiC and TiN additions were prepared by spark plasma sintering (SPS). Their microstructures were studied further by using SEM, TEM, EDX. Hardness (HRA, namely Rockwell Hardness A Scale) and transverse rupture strength (TRS) were also measured. It was found that the cermets sintered by SPS contained many grains with the typical “core–rim” structures, which were believed to form by Ostwald ripening mechanism. The grain size was found to reduce with increasing nanoscale-sized additions. The cermet with all the ceramic powders being nanoscale-sized structure contained many small grains, the sizes of which were less than 100 nm, besides some larger grains with about 200–300 nm size. In addition, when the cermets were sintered by SPS, the addition of nano-powders could improve the mechanical properties of the cermets greatly. In the cermets with nano-additions, some nano-grains were found to be inlaid in the rim of the larger ceramic grains and kept partial coherent with these larger ones. It was the firm joint between them and the reduction of the average size of the grains that led to strengthening and toughening of the cermet with nano-additions.