Removal characteristics of ammonia by a peat biofilter seeded with night soil sludge on a lab oratory scale were investigated. By gradually increasing ammonia load from 0.13 to 3.48 g-N.kg-dry peat(-1).d(-1) and pH control of the peat bed, the removal ratio of ammonia was observed at an average of 95% in a 110-d experiment, and the maximum removal capacity of ammonia reached 3.24 g-N kg-dry peat(-1.)d(-1). This value was about 10 times higher than that in previous reports. As determined by kinetic analysis, maximum removal rate of ammonia, V-m, was 11.4 g-N.kg-dry peat(-1).d(-1) and saturation constant, K-s, was 226 ppm.