In this study, we firstly aimed to use Nb as dopant to dope into the TiO2 lattice in order to narrow band gap energy or enhance photocatalytic activity of the Nb-TiO2. Then, the prepared Nb-TiO2 was combined with g-C3N4 to establish Nb-TiO2/g-C3N4 direct Z-scheme system for superior reduction of CO2 into valuable fuels even under visible light. The obtained results indicated that the band gap energy of the Nb-TiO2 (2.91 eV) was lower than that of the TiO2 (3.2 eV). In the successfully established Nb-TiO2/g-C3N4 direct Z-scheme system, the photo-excited e(-) in the CB of the Nb-TiO2 combined with the photo-excited h(+) in the VB of the g-C3N4 preserving the existence of e(-) in the CB of the g-C3N4 and h(+). in the VB of Nb-TiO2, and thereby, the system produced numerous amount of available e(-)/h(+) pairs for the reduction of CO2 into various valuable fuels. In addition, the produced e(-) of the Nb-TiO2/g-C3N4 existing in the CB of the g-C3N4, which the potential energy is approximately -1.2 V, would be strong enough for the reduction of CO2 to generate not only CH4 and CO but also HCOOH. Among established Nb-TiO2/g-C3N4 materials, the 50Nb-TiO2/50 g-C3N4 material was the best material for the CO2 reduction. (C) 2019 Published by Elsevier Inc.