Significant enhancement in supercapacitor performance has been achieved via a new RuO2 nanocomposite materials prepared by direct ruthenium sputtering on arrayed multi-walled carbon nanotubes supported by Ti-buffered Si wafer. XPS, HRTEM and SAED analyses reveal that as-prepared nanoparticles have a crystalline Ru metal core with RuO2 oxide coating. The nanocomposites convert to RuO2–CNx NTs with subsequent electrochemical cycling. At present, well-dispersed and strongly adhered RuO2 NPs have been densely populated on CNx NTs to obtain the overall specific capacitance (1380 F/g-RuO2), charging–discharging rate (up to 600 mV/s) and operation stability (5000 cycles). Thus, RuO2–CNx NTs nanocomposites would make a promising candidate for use in next-generation high efficiency miniaturized supercapacitors directly fabricated on Si substrate.