Annealing of amorphous precursor-derived Si-B-C-N ceramics for 3 h at 1800 degreesC in 15 bar nitrogen yielded a material consisting of SiC with a mean grain size of about 100 nm, embedded in a turbostratic B-C-N phase. The deformation behavior of this material was investigated by compression tests at 1400 degreesC in air. Dependent on the applied stress the strain rate decreased with time. The deformation rate consists of a stress dependent component that is proportional to the applied stress, which indicates that this part of the deformation mechanism is based on viscous flow. Furthermore, the influence of oxidation on the deformation behavior is investigated.