Molybdenum oxides were synthesized by a hydrothermal reaction at 120-180 degreesC for I day in mixture aqueous solutions of A(2)MoO(4) (A=Li, Na, K) and HCl at various ratios of (H in HCl)/(A in A(2)MoO(4)). The crystal system of resultant products depended on the kinds of A cations because of their different ionic radii. In case of A=Na, molybdenum oxide phases with hexagonal and orthorhombic cells were formed. In case of A=K, we obtained three phases of triclinic, hexagonal, and orthorhombic MoO3-based oxides and their mixtures. When LiMoO4 was used as the starting material, the existence of epsilon-MoO3 and orthorhombic phases was confirmed in the products. They contained some water molecules and A ions in the structure, and their compositions depended on the starting H/A ratio of the hydrothermal solution. The orthorhombic x(Li2O)(.)MoO(3)(.)y(H2O) electrode which was hydrothermally formed from Li2MoO4 system underwent electrochemical lithium intercalation up to Li/Mo = similar to 1.6 [>300 mA h (g oxide)(-1)] on electroreduction until 1.3 V vs. Li metal.