In integrated coal gasification combined-cycle power-generation (IGCC) systems, ammonia in gasified fuel is passed through a hot/dry type gas clean-up facility into a gas turbine. The ammonia is converted to nitrogen oxides in the gas turbine combustion process. Therefore, ammonia removal from coal-gasified fuel effectively reduces NOx emissions in IGCC systems. We clarified the optimum NO/NH3, ratio, the optimum concentration of added O-2, and the influence of CO, H-2, and CH4 in the coal-gasified fuel on NH3 decomposition and NO reduction through experiments using a tubular flow reactor and numerical analysis based on reaction kinetics. The main results were as follows: (1) The optimum NO/NH3 ratio for maximizing NH3 decomposition and NO reduction was about 1. (2) The NH3 decomposition ratio depended only on H-2, and decreased rapidly with increasing Ha concentration. (3) The NO reduction ratio decreased with an increasing H-2 concentration. (3) The remaining CH4 which was not decomposed by pyrolysis, increased with an increasing CH4 concentration and caused the reaction temperature to rise, as opposed to casts of CO and H-2. (5) The method was effective in decreasing total fixed nitrogen (TFN) by up to 40% and minimizing the total concentration of remaining NH3 and NO in air-blown, coal-gasified fuel.