By hot swaging, the nano-composite W-4.5%ThO2 cathode was fabricated. A comparative investigation has been made on the operation characteristics for a conventional W-2%ThO2 cathode, a conventional W-4%ThO2 cathode and a nano-composite W-4.5%ThO2 cathode. The results showed that the arc starting and arc voltage-current characteristic of the nano-composite W-4.5%ThO2 electrode was the best among the three cathodes. These operating characteristics depended on the content and the size of thoria. The anti-erosion ability of the nano-composite W-4.5%ThO2 cathode was slightly better than that of conventional W-4%ThO2 cathode, but was obviously improved as compared to W-2%ThO2 cathode, indicating that the content of thoria governs the resistance to arc erosion of the electrodes. (C) 2003 Elsevier Science Ltd. All rights reserved.