Iridium submicroparticles (SMPs) were prepared at room temperature via a photochemical reduction route in aqueous solution with polyvinylpyrrolidone (PVP) as capping agent. We found that the incident wavelength has a great effect on the growth rate of Ir SMPs. The shorter the wavelength is, the faster the generation of Ir SMPs is. The Ir SMPs were composed of the Ir nanoparticles (NPs), showing discus-like hierarchical structure. The presence of PVP during photochemical synthesis is crucial for the discus-like morphology and the hierarchical structure. The as-prepared Ir SMPs exhibit high catalytic activity, good recyclability and stability for the reduction of methylene blue (MB). Moreover, the hierarchical structure allows the presence of large amounts of Ir NPs as a group, which significantly improves the separation efficiency of the catalyst from reaction media by centrifugation. (C) 2016 Elsevier B.V. All rights reserved.