In Japan, priority of sewage works implementation has gradually been given to smaller communities. Sewage treatment processes for small communities must meet several requirements such as low construction and O-M cost, easy O-M, stable performance, and in some locations nitrogen and/or phosphorus removal as well as BOD and SS removal. With a view to achieving these requirements, the authors have been developing a novel anaerobic/aerobic filter process for simultaneous removal of BOD, SS and nitrogen. In this process, an upflow anaerobic filter is followed by a nitrification tank using entrapped immobilized nitrifier pellets and an aerobic filter for the polishing process. In order to demonstrate this novel process in the field, a pilot plant with a capacity of 1.75 m3/d was installed in an existing sewage treatment plant near Tokyo in January, 1996. The target effluent qualities are BOD and T-N less than 10 mg/l respectively and SS less than 5 mg/l. The pilot plant study has shown that the overall treatment performance of 96∼97% in SS and BOD removal and 74∼75% in T-N removal has been stably obtained under the conditions of 5.5h in total retention time, recycling ratio of 3, and 25 to 250% in load variation.