Photoelectrochemical behavior and Photocatalytic decomposition of Methylene Blue were studied on (Nb,Ti)O2 nanosheets electrode and (Nb,Ti)O2 particles produced from nanosheets, respectively. A detailed characterization of the materials show that Nb-substitution suppresses the transition from anatase to rutile. Depending on the oxygen partial pressure during the transformation, the Nb-substitution into TiO2 provokes different defect situations and also electronic properties. 1% Nb-substitution can drasticly increase the photocurrent and photocatalytic activity of Ti0.9O2 due to the formation of new defects and electron traps that can promote the separation of photoinduced holes and electrons. However, high concentration of electron traps produced by heavy Nb-doping can serve as efficient recombination centers that caused loss of photocatalytic activity of the samples.