ZnO nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method. The morphology, structure, and light absorption properties of PANI-ZnO composites were examined by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis spectra. UV–vis spectra reveal that PANI-ZnO composites showed stronger absorption than neat ZnO under the whole range of visible light. New characteristic peaks were found in PANI-ZnO composites according to the X-ray diffraction patterns after hybridization of PANI and ZnO, which indicating that there was a strong interaction between PANI and ZnO nanoparticles. The resulting PANI-ZnO composites exhibit significantly higher photocatalytic activity than that of neat ZnO for degradation of anthraquinone dye (reactive brilliant blue KN-R) aqueous solution under visible light irradiation (λ > 420 nm).