A core-shell hybrid material of amorphous hydrous RuO2-coated carbon nanotubes (CNT–RuO2) with a RuO2 loading as high as 82.4wt% was prepared by a solution method using RuCl3 and NaHCO3 aqueous solutions. The effect of preparation conditions, especially the dripping speed of the NaHCO3 solution, on the formation of the core-shell structure was investigated, and the corresponding mechanism was discussed. Supercapacitive properties of the CNT–RuO2 and amorphous hydrous RuO2 electrodes with a thickness of over 200μm were studied and the crucial factors to govern their rate capability were analyzed. For the thick CNT–RuO2 electrode, a comparison of its specific capacitance before and after subtracting the effect of the voltage drop of discharge curves caused by the inner resistance of the CNT–RuO2 symmetrical supercapacitor indicates that electronic conductivity is more important than proton diffusion in determining its rate capability.