In this study, Ce0.75Zr0.25O2 mixed oxide catalysts and with 1, 5 and 10 wt% Nb-doped were prepared via urea hydrolysis and tested for methane oxidation. The XRD patterns of Ce0.75Zr0.25O2 mixed oxide catalysts and Nb-doped indicate a cubic fluorite structure. The evidence for extra peaks due to non-incorporated Nb was not observed in any XRD patterns of Nb-doped Ce0.75Zr0.25O2. The Raman spectra of niobium oxide surface species were found in 1 wt% Nb loading. The incorporation of 1 wt% Nb was found to promote the reduction of Ce0.75Zr0.25O2 mixed oxide whereas increasing the amount of Nb (5 and 10 wt%) retarded surface reduction. The methane oxidation activity of the mixed oxides was apparently dependent on Nb loading, which relates to the degree of reducibility. In general the catalytic activity decreased with increasing Nb content (above 1 wt%). Nevertheless, it was found that 1 wt% Nb loading promotes the catalytic activity of Ce0.75Zr0.25O2 mixed oxides.