Cocatalysts are usually needed to improve photoconversion efficiency in water splitting with heterogeneous photocatalysts. Here, we show that NiOx (0 < x < 1) nanoparticles loaded on a layered perovskite, BaLa4Ti4O15 (BLT), serve as an effective electron sink. We have measured the time profiles of transient absorption (TA) of BLT with and without loading NiOx cocatalyst in air and in water in a wide wavelength range from 400 nm to 4 mu m upon excitation with a femtosecond pulse at 266 nm. TA at 4 mu m indicates that photogenerated electrons are rapidly transferred to cocatalyst within 1 ps. The time profile of TA at 402 nm from sub-mu s to 10 ms contributed by surface photoholes is affected by loading of cocatalyst and redox reactions with water. Fittings of the decay profiles of TA at 402 nm with a trap-detrap kinetic model indicate that the oxidation of water appreciably starts at around 1 ms after the pump pulse, while the reduction of water takes place prior to oxidation in much early time domains. This implies that the redox reactions take place under substantial imbalance between electron and hole densities.