Hydrous ruthenium oxides (RuO2.xH(2)O) with different contents of water (x) were prepared by annealing commercial RuO2.2.6H(2)O powders at different temperatures. The morphologies and crystalline structures of RuO2.xH(2)O were investigated using transmission electron microscope (TEM) and selected area electron diffraction (SAED) techniques. From the TEM images, it was observed that the particle size of RuO2.xH(2)O increased with increasing annealing temperature. From the SAED patterns, it was observed that RuO2.xH(2)O powders became an amorphous phase at annealing temperatures <116 degreesC and became a crystalline phase at annealing temperatures above 116 degreesC. Amorphous RuO2.xH(2)O prepared at 116 degreesC reached its maximum specific capacitance as a result of proton insertion into the bulk of RuO2 but with smaller Ru-Ru distance in the local structure. The more disordered structure induced by proton insertion was obtained by SAED pattern from a sample annealed at 116 degreesC. The possible connection between the microstructure and specific capacitance of RuO2.xH(2)O is discussed.