Single-crystalline WO 3 nanowires were synthesized on carbon papers through a chemical vapor deposition process without using any catalysts. WO 3 nanowire field-effect transistors (FETs) were constructed to discuss the mechanism of electronic transport based on a thermal-activation model and a displacive transition. Photoconductive measurements showed that individual WO 3 nanowire photodetector was sensitive to the ultraviolet light, and the photoresponse was further improved using WO 3 nanowires on carbon papers, demonstrating significantly shortened response and decay times, and enhanced stability. Field-emission measurements showed that WO 3 nanowires were excellent field-emitters: an ultralow turn-on field of 1.8 V mm À1 and a threshold field of 3.3 V mm À1 , and a high field-enhancement factor of 6.9 Â 10 3 . These results indicate that present unique WO 3 nanowires on carbon papers are promising candidates for constructing high-performance electronic and optoelectronic devices.