Porous CeO2/sulfur-doped g-C3N4 (CeO2/CNS) composites were synthesized by one-pot thermal condensation of thiourea and cerium nitrate as starting materials. The obtained CeO2(x)/CNS composites (x = 8.4, 9.5 and 10.4 wt%) with different CeO2 contents were characterized by the XRD, FT-IR, XPS, TEM, BET, DRS and PL analyses. The TEM images displayed a nonporous and platelet-like morphology for pure CNS but a nanoporous structure with numerous uniform pore sizes of similar to 40 nm for the CeO2(9.5)/CNS composite. The XRD phase structures and TEM morphologies confirmed that structural evolution trend and stacking degree of CNS were disrupted in precense of the CeO2 nanoparticles. The optimized photocatalyst, i.e. CeO2(9.5)/CNS nanocomposite, exhibited the highest visible light photocatalytic activity (91.4% after 150 min) with a reaction rate constant of 0.0152 min(-1) toward methylene blue (MB) degradation which was greater compared with the individual CNS (0.0044 min(-1)) and CeO2 (0.0031 min(-1)) photocatalysts. This enhanced photocatalytic performance was originated from heterojunctions formed between CeO2 and CNS that improved the effective charge transfer through interfacial interactions between both components. The heterojunction prepared displayed excellent stability for the photocatalytic activity under the optimized conditions including catalyst dosage 0.08 g, initial dye concentration 7 mg/L and irradiation time 150 min which was obtained using response surface methodology (RSM). The trapping experiments using isopropanol, benzoquinone and ethylenediaminetetraacetic as the center dot OH, center dot O-2(-) and h(+) scavengers, respectively, verified that the center dot OH and center dot O-2(-) as major species directly attacked onto the MB molecules while h(+) showed a negligible role. Finally, it could be stated that simultaneous doping of both sulfur and CeO2 within the g-C3N4 structure using a simple one-pot synthetic process produced very active photocatalysts illustrating their potential for practical applications in industrial water treatment purposes. (C) 2017 Elsevier Inc. All rights reserved.