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.