Well-dispersed zinc oxide/cyclized polyacrylonitrile (ZnO/CPAN) nanocomposites were prepared by a facile in-situ precipitation method. The mixture solution of dimethyl sulfoxide containing zinc nitrate and polyacrylonitrile (PAN) was added dropwise into ammonia water under vigorous magnetic stirring. Accompanied by the precipitation of PAN in water, zinc hydroxide were simultaneously formed via in-situ reaction of zinc nitrate with hydroxyl ions, leading to the uniform dispersion of zinc hydroxide nanoparticles in the precursor of ZnO/PAN nanocomposites. Then ZnO/CPAN nanocomposites were prepared by calcining the obtained precursor at 250 degrees C in nitrogen atmosphere via cyclization/dehydrogenation reaction of PAN and decomposition reaction of Zn(OH)(2). The as-prepared ZnO/CPAN nanocomposites were characterized by XRD, SEM, XPS, UV-vis DRS, PL, etc. Results show that CPAN molecules in ZnO/CPAN nano composites significantly decrease the mean size of ZnO nanocrystals, increase the quantity of oxygen defects in ZnO particles, improve the absorbance of ZnO in the whole wavelength range especially in the visible-light range, and obviously reduce the recombination probability of photo-generated electron/hole pairs. The photocatalytic activity of ZnO/CPAN nanocomposites was evaluated by photodegradation of methyl orange (MO) solution under visible light irradiation. Experiment results reveal that the apparent rate constant k of MO photodegradation under visible light irradiation photocatalyzed by ZnO/CPAN (0.361 h(-1)) is 1.28, 5.84 and 25.8 times of that by AgBr (0.282 h(-1)), Ag3PO4 (0.0618 h(-1)) or g-C3N4 (0.0140h(-1)), respectively, meaning that ZnO/CPAN exhibits much higher visible-light photocatalytic activity than these typical visible-light photocatalysts. The visible-light photocatalytic mechanism has been discussed. (C) 2016 Elsevier B.V. All rights reserved.