The deformation behavior of boron- and carbon-doped beta-silicon carbide (B,C-SiC) with an average grain size of 260 18 nm containing 1 wt% boron was investigated by compression testing at elevated temperatures. Extensive grain growth during deformation was observed. The stress-strain curves were compensated for grain growth by assuming power-law type of dependence on grain size and strain rate. The stress exponent n was similar to1.3 and the grain size exponent p was similar to2.7 at temperatures ranging from 1593 to 1758 C. The apparent activation energy of deformation Q(d) was similar to760 kJ/mol, which was lower than the activation energy for lattice diffusion of silicon and carbon in SiC and higher than that for grain-boundary diffusion of carbon in SiC. These results suggest that the deformation mechanism of the fine-grained B,C-SiC is grain-boundary sliding accommodated by the grain-boundary diffusion.