Previous research has shown that nitrogen in municipal wastewater could be eliminated by a biofilter system. This study investigates the effect of the recycle ratio on total nitrogen removal and the nitrogen component in the effluent. In this study, a system combining pre -denitrification/nitrification biofilters was set up. The experiments which varied the recycle ratio of the nitrifying solution to the influent were carried out in order to determine the amount of the total nitrogen removal and the form of nitrogen in the effluent. These experimental results show that total nitrogen removal might be dependent on nitrification but not on denitrification. Although the operation at a low recycle ratio would result in a lower value of total nitrogen removal, the NH3-N content of the effluent would be lower and the flow condition would be more stable. In comparison, operation at a higher recycle ratio would result in a lower NO3-N content in the effluent, while the NH,-N content in the effluent would be higher. At a recycle ratio of 2.5, the total nitrogen removal is at its maximum. The relationship between specific nitrification rate and recycle ratio is also discussed.