Pulp and paper industry generates large volumes of highly heterogeneous wastewaters containing compounds from wood or other raw material, process chemicals as well as compounds formed during processing. This study has designed a fixed film reactor which uses the concept of biological attached growth treatment to treat the pulp and paper wastewater. The laboratory-scale fixed film reactor is designed with a circular column of 120 cm height, 15 cm inner diameter and a total volume of 23000 cm 3 . The column which constructed in PVC was packed with PVC plastic pipes which were cut into the size of 4.5 cm length and 3 cm diameter and had a specific surface area of 42 cm 2 . An amount of 150 PVC plastic pipes were placed in the digester. The system was found could remove about 53% of BOD 5 and 89% COD. The treatability constant corresponding to the depth of the reactor, k in this study is found to be 0.038 gal/min 0.5 ft and the observed reaction rate constant, K is 0.04 ft/d at 25°C. This fixed-film reactor could be operated as a trickling filter.