ABSTRACT: Single-walled carbon nanotubes (SWCNTs) with large diameters (LDs) ($3 nm) have wide applications. But, up to now, the synthesis of these novel nanostructured carbon materials is still a great challenge, and exploration of a simple synthesis method suitable for economical and large-scale production is still an important task. The present study reports on the continuous synthesis of SWCNTs with a large average diameter of 5.8 nm and a maximum diameter of 10 nm. Raman spectroscopy is used to show the first observation of peaks at low frequencies of 45–85 cm 1 associated with the observed LDSWCNTs but the peaks at higher frequencies of 200–270 cm 1 for the small-diameter (SD) counterparts. After purification by a non-destructive approach, the present LD-SWCNTs are found to be dispersible in water, a property which will benefit many applications. This observation is in contrast to that for conventional SD-SWCNTs which cannot be dispersed in any solutions without complicated functionalization. When LD-SWCNTs are used as a catalyst support for fuel cells, they show much better performance than SD-SWCNTs, multi-walled CNTs and the commercial catalyst from Johnson Matthey Co. It is suggested that the present approach may be immediately applied for large-scale production and the applications of LD-SWCNTs in a wide range of areas such as information technology, biomedicine, and environmental and energy industries may be investigated.