The C3N4/BiOIO3 composites with heterostructures have been fabricated by simply depositing BiOIO3 on the surface of C3N4 at hydrothermal conditions, using bismuth nitrate and potassium iodate as precursors. C3N4 is an excellent organic semiconductor, which can be excited by visible light. BiOIO3 is a layered bismuth-based compound that has an internal polar field. Coupling C3N4 with BiOIO3 can combine the advantages of the two compounds and obtain better photocatalytic properties. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transformation infrared spectra have been carried out to confirm the structures and morphologies of as-prepared products. The absorption properties have been characterized by diffuse reflectance spectra and the photocatalytic activities have been evaluated by photodegradation of methyl orange, Rhodamine B and 2,4-dichlorophenol. Compared with C3N4, all C3N4/BiOIO3 composites exhibit better visible-light-driven photocatalytic properties. It is a synergetic effect that enables the composites to harvest light and promote charge separation, which eventually leads to the enhancement of the photocatalytic efficiencies. Under UV-vis light irradiation, C3N4/BiOIO3 composites also exhibit better activities, and the charge transfer process is similar to a redox mediator-free Z-scheme system. (C) 2014 Elsevier Inc. All rights reserved.