Iron titanate (Fe2TiO5) is a promising photoanode material due to a narrow band gap, appropriate band edges, robustness and abundance. However, its performance is limited because of its low conductivity and short hole diffusion length. Precisely controlled, a few Fe2TiO5 layers of inverse opal structure (IOS) is fabricated via a layer-by-layer self-assembly and then treated by hybrid microwave annealing to produce a highly crystalline, yet IOS morphology-preserved Fe2TiO5 photoanode film for solar water splitting. The highly transparent Fe2TiO5 IOS film shows a greatly enhanced visible light harvesting, higher density of catalytically more active crystal planes, and many single crystalline nanoplates grown on the IOS architecture, relative to a reference planar film prepared under similar conditions. As a result, the optimized ‘exactly’ three Fe2TiO5 layers IOS electrode with a sacrificial gallium oxide underlayer and a ternary (Ni2CoFe)OOH co-catalyst records 2.08 mA cm−2 at 1.23 VRHE under 1 sun (100 mW cm−2) irradiation, which is the highest photocurrent density produced by Fe2TiO5 photoanode up to date.