RuO2-cocatalyst-loaded ALi(2)Ti(6)O(14) (A: 2Na and Sr) with a unique tunneling structure shows photocatalytic activity for water splitting into H-2 and O-2 in stoichiometric amounts under UV irradiation. The addition of LiOH in the reactant solution, to replenish Li+ defects within the tunneling structure, improved the photocatalytic activities of ALi(2)Ti(6)O(14) (A: 2Na and Sr) by approximately 10 and four times, respectively.