This study reports a delicate electroless approach for the deposition of RuO 2 ·nH 2 O nanoparticles on the VO x ·mH 2 O nanowires and this method can be extended to deposit RuO 2 ·nH 2 O nanoparticles on various material surfaces. Electrochemical characterizations, including linear sweep voltammetry (LSV), electrochemical quartz crystal microbalance (QCM) analysis and rotating ring-disc electrode (RRDE) voltammetry, were carried out to investigate the growth mechanism. The deposition involves the catalytic reduction of dissolved oxygen by the V 4+ species of VO x ·mH 2 O, which drives the oxidation of RuCl 3 to proceed with the growth of RuO 2 ·nH 2 O. This core/shell VO x ·mH 2 O/RuO 2 ·nH 2 O shows a better catalytic activity of the oxygen reduction reaction (ORR) than RuO 2 ·nH 2 O, which is ascribed to the pronounced dispersion of RuO 2 ·nH 2 O. Such an electroless approach was applicable to the preparation of a RuO 2 -based nanoparticle suspension as well as the deposition of nanocrystalline RuO 2 ·nH 2 O on other functional supports like TiO 2 nanowires. The thus-obtained RuO 2 -decorated TiO 2 nanorods exhibit significantly an enhanced photoactivity toward photoelectrochemical water oxidation. The versatility of the current electroless approach may facilitate the widespread deployment of nanocrystalline RuO 2 ·nH 2 O in a variety of energy-related applications.