This work presents a study on the controlled growth of WO3 nanowires via chemical vapor deposition without catalyst, and their potential applications in visible photodetectors. The influence of growth conditions on the morphology of WO3 nanowires is studied in order to understand the growth mechanism of WO3 nanowires, and ultra-long (60 [Formula: see text], the longest one ever reported) WO3 nanowires with a spindle shape are achieved by optimizing the growth conditions. It was found that the length of WO3 nanowires increases from 15 [Formula: see text] to 60 [Formula: see text] with increasing the argon carrier gas flow rate from 30 sccm to 90 sccm, and then saturates with further increasing the argon carrier gas flow rate. However, the length of WO3 nanowires reduces from 60 [Formula: see text] to 19 [Formula: see text] with increasing the tube inner pressure from 2.5 Torr to 3.5 Torr. The photoconductor detectors based on WO3 single nanowires present excellent device performance with a responsivity as high as 19 A W-1 at a bias of 0.1 V, a detectivity as high as 1.06 × 1011 Jones, and a response (rising and decay) time as short as 8 ms under the illumination of a 404 nm laser. These results indicate the great potential of WO3 nanowires for applications in fabricating high performance visible photodetectors.