Abstract: A biological oxidation filter system can be used as a pretreatment process in water treatment, or for processing sewage or wastewater by reproducing the purification mechanisms in nature environments. It has a physical screening function and an oxidation function through the aeration and biological decomposition. The biological oxidation filter system includes: a raw water inflow unit; a biological contact filter unit; a filtrate outflow unit; an oxidation air supply unit supplying air and/or oxygen in order to provide a proper growth environment for microbial flora and perform the oxidation in the biological contact filter unit; and an air backwashing unit and a water back washing unit for backwashing the filter media when the biological contact filter unit is blocked.