Electrically conducting aramid/polypyrrole (PPy) composite fibres were prepared by vapour-phase polymerization of pyrrole using FeCl3 . GH(2)O as an oxidant. Conducting stability and mechanical properties were investigated and the change of electrical resistance due to the applied strain and its recovery were analysed. Composite fibres showed a good thermal stability in conductivity within a range of 170 degrees C. The mechanical properties of conducting composite fibres were affected slightly by polymerization of pyrrole, and could maintain good mechanical properties of the original aramid fibre. The modulus increased slightly with polymerization of pyrrole, and tenacity decreased only slightly. The electrical resistance of the composite fibres initially increased slowly with increasing elongation, but increased sharply near breaking point. The residual electrical resistance appeared on removal of the applied strain. This indicates the possibility of the application of conducting aramid/PPy composite fibres as an intelligent material.