Highly single-crystalline ruthenium dioxide (RuO2) nanoneedles were successfully grown on polycrystalline electrospun titanium dioxide (TiO2) nanofibers for the first time by a combination of thermal annealing and electrospinning from RuO2 and TiO2 precursors. Single-crystalline RuO2 nanoneedles with relatively small dimensions and a high density on electrospun TiO2 nanofibers are the key feature. The general electrochemical activities of RuO2 nanoneedles-TiO2 nanofibers and Ru(OH)(3)-TiO2 nanofibers toward the reduction of [Fe(CN)(6)](3-) were carefully examined by cyclic voltammetry carried out at various scan rates; the results indicated favorable charge-transfer kinetics of [Fe(CN)(6)](3-) reduction via a diffusion-controlled process. Additionally, a test of the analytical performance of the RuO2 nanoneedles-TiO2 nanofibers for the detection of a biologically important molecule, hydrogen peroxide (H2O2), indicated a high sensitivity (390.1 +/- 14.9 mu A mM(-1) cm(-2) for H2O2 oxidation and 53.8 +/- 1.07 mu A mM(-1) cm(-2) for the reduction), a low detection limit (1 mu M), and a wide linear range (1-1000 mu M), indicating H2O2 detection performance better than or comparable to that of other sensing systems.