Direct ozone (O 3 ) injection is a promising flue-gas treatment technology based on oxidation of NO and Hg into soluble species like NO 2 , NO 3 , N 2 O 5 , oxidized mercury, etc. These product gases are then effectively removed from the flue gases with the wet flue gas desulfurization system for SO 2 . The kinetics and mixing behaviors of the oxidation process are important phenomena in development of practical applications. In this work, planar laser-induced fluorescence (PLIF) of NO and NO 2 was utilized to investigate the reaction structures between a turbulent O 3 jet (dry air with 2000ppm O 3 ) and a laminar co-flow of simulated flue gas (containing 200ppm NO), prepared in co-axial tubes. The shape of the reaction zone and the NO conversion rate along with the downstream length were determined from the NO-PLIF measurements. About 62% of NO was oxidized at 15d (d, jet orifice diameter) by a 30m/s O 3 jet with an influence width of about 6d in radius. The NO 2 PLIF results support the conclusions deduced from the NO-PLIF measurements.