The effects of turbulence intensity of an ambient air flow on flame structure and NOx formation were investigated experimentally in hydrogen/air nonpiemixed flames. To identify the effect of sole turbulence intensity, a new combustor with a turbulence generator, which can increase the turbulence intensity of air stream under the condition of an identical mean velocity, was adopted. The experiment was conducted with and without the turbulence generator for the two fuel cases of H-2: N-2 = 1: 1 and H-2: N-2 = 1: 2, by volume. As a result, as the turbulence intensity increased, the reducing effect of NOx was more significant in the condition of a higher flame temperature. In addition, the conversion ratio from NO to NO2 increased. Two major factors can reduce the production of NOx as the turbulence intensity increases: significant NOx reduction corresponding to about 70% was found in the upstream region due to the increase in the strain rate effect and in the downstream region due to the rapid mixing effect. From these results, it is possible to conclude that adjustment of turbulence intensity is a very useful method to reduce NOx emission in hydrogen nonpremixed jet flames. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.