In this work, poly(sodium-4-styrene sulfonate) (PSS)-functionalized multi-walled carbon nanotubes (FMWCNTs) were first synthesized via a polymer-assisted technique. Then, Ru0.58In0.42Oy center dot nH(2)O nanoparticles (NPs) were mono-dispersed onto the FMWCNTs surfaces under mild hydrothermal condition. Here, PSS with negative charge serves as a bifunctional molecule both for solubilizing and dispersing MWCNTs into aqueous solution and for tethering Ru3+ and In3+ to facilitate the good dispersion of Ru1-xInxOy center dot nH(2)O NPs onto their surfaces. The good dispersion of Ru0.58In0.42Oy center dot nH(2)O NPs onto FMWCNTs makes OH- ions and electrons easily contact these NPs with abundant electroactive sites, which results in a large specific capacitance (SC) of 319 F g(-1) for the naocomposites. Moreover, a symmetric electrochemical capacitor (EC) is constructed by using the nanocomposites as electrodes and delivers large specific energy density of 18.1 Wh kg(-1), desirable power property of 1302 W kg(-1), high electrochemical reversibility and good SC retention of 84.7%. (C) 2010 Elsevier Inc. All rights reserved.