A new and effective process, surface nitridation by hot isostatic pressing (HIP), has been successfully developed to enhance the mechanical properties of some carbide and carbide-containing ceramics. Mechanical properties of SiC monolithic ceramics and some SiC-containing composites before and after HIP nitridation are compared and discussed. The strengthening and toughening mechanism and HIP nitridation model are proposed according to theoretical calculation and experimental analysis.