Biofilteration technology for the removal of pollutants from air streams is unregarded in our country. This method is applied to polluted air streams with high flowrate and low concentration of pollution, and economic in comparision with other methdos such as catalytic oxidation or gas absorption. This method is not only simple, but also it is a low energy consumption method, without secondary polllutants. In the present reaserch, a bench scale biofilter for removal of ammonia from air was designed and constructed. During 4 months continuos operation of the biofilter, its performance was evaluated under various inlet pollutant concentrations and polluted air flowrates, as effective operational parameters. Results have shown that biofilter removal efficiency is affected by various prameters such as temperature, water content of bed, and input pulses. The biofilter minimum, maximum and average of efficiency under steady state conditions were 99.8%, 91.4% and 97.5%, respectively. In addition, the complete removal capacity, and the maximum removal capacity of the biofilter were 6 and 11.6 g NH 3 /(m 3 bed volume )/ h, respectively. Mass transfer coefficient of the biofilter, and the maximum biodegradation rate of the microbial culture were determined at 0.24 h -1 and 3.7 g NH 3 /(m 3 bed.volume) / min, based on regression of the experimental. The presented model predicts the experimental data accordingly, and its maximum difference with the reported experimental results of Taghipour et. al., and Chen et. al. are 9.4% and 3.6% respectively