Two types of Si-Ti-C-O fibres were heat treated in a preheated graphite furnace at temperatures between 1273 and 1973 K, and the change in the electrical resistivity was measured after removing the fibres from the furnace. The resistivity of the fibres decreased monotonically with increasing heat-treatment temperature, but showed a significant increase of the order of 10(1)-10(2) in the temperature range of gas evolution from the fibres. The resistivity of the fibre which has an amorphous character began to increase at a lower temperature than that of the fibre with a crystalline character. This increase in resistivity did not occur during heat treatment in a pure oxygen atmosphere, because the oxide layer formed on the fibre surface suppressed gas evolution from the fibres. The X-ray diffraction patterns of heat-treated fibres in nitrogen or oxygen atmospheres revealed that beta-SiC crystals began to precipitate from the amorphous state as the heat-treatment temperature increased. The beta-SiC crystal growth, however, did not always correspond with the decrease in the fibre resistivity.