The thermal conductivity of a SiC ceramic was measured as 270 W(.)m(-1.)K(-1) at room temperature. At low temperatures (T < 25 K), the decrease in the conductivity was proportional to T-3 on a logarithmic scale, which indicated that the conductivity was controlled by boundaries. The calculated phonon mean free path in the ceramic increased with decreased temperature, but was limited to similar to4 mum, a length almost equal to the grain size, at temperatures below 30 K. We concluded that the thermal conductivity of the ceramic below 30 K was influenced significantly by grain boundaries and grain junctions.