The combustion of biomass of various nitrogen contents and its NO emission were investigated experimentally in this study. All the experiments were conducted in an I.D. 0.45 m pilot-scale vortexing fluidized bed combustor (VFBC). Rice husk, corn, and soybean were used as feeding materials. Urea was added into the feeding materials for the purpose of adjusting nitrogen content. The effects of various operating parameters on NO emission, such as bed temperature, excess air ratio, and flow rate of secondary air, were investigated. The effects of nitrogen content of fuels on NO emissions were also investigated by using the mixtures of rice husk/soybean, rice husk/urea, corn/soybean, and corn/urea in various weight ratios. The NO concentrations at various positions in the combustor were sampled and recorded. The experimental results show that most nitric oxide is formed at just above the bed surface. Temperature and excess air ratio are the major operating parameters for NO emission. For biomass with high nitrogen content. NO emission decreases with excess air, and increases with bed temperature. Compared with char-N, volatile-N is the more dominant reactant source for NO emission. (C) 2010 Elsevier Ltd. All rights reserved.