In this study, a series novel NaNbO3/Bi2WO6 heterojunction composites with a type-II alignment were fabricated via a facile we impregnation method. The as-prepared photocatalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis spectroscopy (DRS), photocurrent (PC) and electrochemical impedance spectroscopy (EIS) analyses. The 30 wt% NaNbO3/Bi2WO6 composite exhibited the best performance in the case of degrading rhodamine B (RhB) aqueous solution under visible light irradiation (lambda > 410 nm), which was similar to 2.5 times and similar to 40 times that of pure Bi2WO6 and NaNbO3, respectively. The improved photocatalytic performance was further demonstrated by 2-chlorophenol under the same reaction conditions. This may be attributed to the enhanced electron-hole separation efficiency in Bi2WO6 with the assistance of NaNbO3, as well as the dye-sensitization effect of RhB dye itself. Intermediates produced during the reaction and RhB degradation pathway were investigated as well. Radical quenching experiments revealed h(+) played the predominant role; O-2(center dot-) functioned as well to some degree. Based on experimental results, the potential functioning mechanism was proposed, which is different from previously reported type-II heterostructure systems when Bi2WO6 works as the electron reservoir and O-2(center dot-) is one of the dominant active species. The as-prepared photocatalyst composite exhibited excellent stability after repetitively running five times. Effects of several operating parameters on the catalyst performance including initial RhB concentration, catalyst dosage, reaction temperature and initial pH were also discussed. This study provides solid evidence for NaNbO3 to be a promising candidate for photocatalysis and gives out a novel photocatalytic mechanism of Bi2WO6-based heterostructures.