The photocatalytic properties for water decomposition of RuO2-dispersed alkaline earth metal and lanthanum indates with an octahedrally coordinated In3+ ion of d(10) configuration were studied. The influences of preparation methods, calcination temperature, and the amount of RuO2 on the activity of RuO2-dispersed CaIn2O4 were examined, and it was shown that the combination of well-crystallized CaIn2O4 with highly dispersed RuO2 particles led to high photocatalytic performance: hydrogen and oxygen were stably produced at nearly the stoichiometric ratio under UV irradiation. The photocatalytic activity of RuO2-dispersed Sr1-xCaxIn2O4 (x = 0.25 0.50, 0.75) increased monotonically with increasing x. The activity of RuO2-dispersed Sr0.93Ba0.07In2O4 was similar to that of RuO2-dispersed SrIn2O4, whereas RuO2-dispersed LaInO3 had much lower activity. The photocatalytic properties of different kinds of indates were compared.