Nitrogen doped bismuth niobate (N-Bi3NbO7) hierarchical architectures were synthesized via a facile two-step hydrothermal process. XRD patterns revealed that the defect fluorite-type crystal structure of Bi3NbO7 remained intact upon nitrogen doping. Electron microscopy showed the N-Bi3NbO7 architecture has a unique peony-like spherical superstructure composed of numerous nanosheets. UV-vis spectra indicated that nitrogen doping in the compound results in a red-shift of the absorption edge from 450 nm to 470 nm. XPS indicated that [Bi/Nb]-N bonds were formed by inducing nitrogen to replace a small amount of oxygen in Bi3NbO7-xNx, which is explained by electronic structure calculations including energy band and density of states. Based on observations of architectures formation, a possible growth mechanism was proposed to explain the transformation of polyhedral-like nanoparticles to peony-like microflowers via an Ostwald riping mechanism followed by self-assembly. The N-Bi3NbO7 architectures due to the large specific surface area and nitrogen doping exhibited higher photocatalytic activities in the decomposition of organic pollutant under visible-light irradiation than Bi3NbO7 nanoparticles. Furthermore, an enhanced photocatalytic performance was also observed for Ag/N-Bi3NbO7 architectures, which can be attributed to the synergetic effects between noble metal and semiconductor component. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.