For heavy-duty gas-turbine engines, one of the promising approaches to reducing NOX emissions is the adoption of lean premixed combustion. This technique could be combined with the conventional technique of exhaust gas recirculation (EGR). However, the reduction in the oxygen concentration will influence the burning velocity and reaction zone characteristics of the lean premixed flame. To elucidate this effect, in this study, we measured the lean premixed flame temperature and OH concentration distributions for various oxygen concentrations instantaneously and simultaneously using laser imaging techniques. Based on the results, we investigated the characteristics of a lean premixed flame under various oxygen concentrations and found that the OH laser-induced fluorescence (LIF) intensity in the reaction zone decreased with the oxygen concentration, as did the flame temperature at a given axial distance from the exit nozzle. The characteristics of the premixed flame changed from a small-scale convexo-concave surface to a smoother one, leading to a decrease in the ratio of turbulent to laminar burning velocity. In addition, local extinction of the premixed flame was observed under conditions with a high air ratio and low oxygen concentration.