We developed the fabrication of three-dimensional (3-D) aligned mesoporous iron oxide nanopyramid arrays (NPAs) by a facile interfacial oriented growth and self-assembly process. The unique NPAs possess a 3-D mesostructure with multiple features, including high surface area (~ 175 m2/g), large pore size (~ 20 nm), excellent flexibility (bent over 150 times), and scalability at foot-scale for practical applications. More importantly, these NPAs structures enable versatile enhancement of localized surface plasmon resonance and photoelectrochemical conversion. The integration of plasmonic gold with 3-D NPAs remarkably improves the performance of photoelectrochemical conversion, leading to ~ 6- and 83-fold increases of the photocurrent under simulated solar and visible light illumination, respectively. The fabrication and in-vestigation of NPAs provide a new paradigm for preparing un-conventional mesoporous oriented thin films, and further suggest a new strategy for designing plasmonic metal/semiconductor systems to for effective solar energy harvesting.