In this study, catalytic removal of NH3 in simulated producer gas from biomass gasification has been experimentally investigated using H-2-reduced titanomagnetite (Fe2.9Ti0.1O4) in a lab-scale fluidized bed reactor at temperatures of 500 and 750 degrees C, respectively. Effects of gaseous species and their combination on the NH3 removal were examined by using seven gas mixtures: (1) Simulated producer gas (H-2, CO, CO2, and CH4); (2) H-2 in Ar; (3) CO in Ar; (4) CO2 in Ar; (5) CH4 in Ar; (6) H-2, CO, and Ar; and (7) H-2, CO, CO2, and Ar. In these test gases, the NH3 concentration was 2300 +/- 200 ppmv. The experimental results show that temperature has a significant effect on NH3 decomposition in all of the tested gases, and the reduced titanomagnetite had a much higher activity at 750 degrees C than at 500 degrees C. In the simulated producer gas, the NH3 decompositions were 28.4 and 94.7% at 500 and 750 degrees C, respectively. Side reactions including the reverse water gas shift reaction, the (reverse) Boudouard reaction, the (reverse) carbon methanation reaction, and the iron oxidization reaction were involved during the NH3 decomposition. Negative effects by gas species in the simulated producer gas on NH3 decomposition were attributed to the equilibrium concentration of H-2, carbon deposition from the Boudouard reaction and carbide formation, and alpha-Fe phase oxidization. However, CH4 was found to have only a slight effect on NH3 decomposition. H-2 in the simulated producer gas was also found to promote carbon formation by the reverse water gas reaction. In the meantime, H-2 also had favorable effects of protecting the alpha-Fe phase on the catalyst from oxidizing by CO2 and hindering carbon formation from CH4 decomposition. Furthermore, CO2 also had a positive effect of inhibiting carbon formation from the Boudouard reaction.