The effect of substitution of Zr for Ti in KLaTiO4 with a layered perovskite structure has been studied on the photocatalytic decomposition of water under the UV light irradiation. Both the optical property and the crystallinity of KLaTiO4 were varied by the substitution of Zr for Ti. As Zr content was increased, the crystallinity of KLaZrxTi1-xO4 was increased, which had a positive effect on the photocatalytic activity in the water splitting reaction. However, the direct band gap property was lost gradually with increase of Zr content, which resulted in lowering the photocatalytic activity. As a result, the highest activity was obtained for KLaZr0.3Ti0.7O4. Although the absorption coefficients of photons for KLaZr0.1Ti0.9O4 and KLaTiO4 were higher than those for KLaZr0.3Ti0.7O4, the crystal structure was disordered, which resulted in lowering the activity. The nickel-loaded catalysts showed a higher activity than unloaded perovskites by a factor of greater than 2.