Ion doping is one of the most effective ways to develop photocatalysts by creating impurity levels in the energy band structure. In this paper, novel Bi3+ doped SrMoO4 (SrMoO4:Bi3+) nanocrystals were prepared by a simple hydrothermal method. By systematic characterizations using x-ray diffraction, infrared spectra, UV-vis spectra, X-ray photoelectron spectroscopy and transmission electron microscopy, it is demonstrated that all the samples crystallized in a single phase of scheelite structure, and particle sizes of SrMoO4:Bi3+ gradually decreased. The Bi3+ doped nanoparticles showed lattice contraction, and band gap narrowing. The photocatalytic activity of the samples was measured by monitoring the degradation of methylene blue dye in an aqueous solution under UV-radiation exposure. It is found that SrMoO4:Bi3+ showed excellent activity toward photodegradation of methylene blue solution under UV light irradiation compared to the pure SrMoO4. These observations are interpreted in terms of the Bi3+ doping effects and the increased the surface active sites, which results in the improved the ratio of surface charge carrier transfer rate and reduced the electron-hole recombination rate. These results illustrate the potential of particle size and surface defect regulation for the construction of novel semiconductor oxide photocatalysts by ion doping. (C) 2016 Elsevier B.V. All rights reserved.