Laboratory investigation was conducted to evaluat the mixing effects on organic removal efficiency to treat low-strength synthetic wastewater using modified anaerobic filter reactor combining anaerobic filter and upflow anaerobic sludge blanket. Using the modified process the low-strength wastewater like municipal sewage could be treated with 85% T-COD removal efficiency at hydraulic retention time of 6 hours. At the constant organic loading of 0.5㎏ COD/㎥-day, the organic removal efficiency and effluent COD concentration are increased as influent COD concentration increased from 125 ㎎/ℓto 500 ㎎/ℓ. Mixing effects on organic removal efficiency are evident and optimum mixing speed is found as 50RPM. Placing the granular studge and media on which slime layer was pre-formed into the reactor seemed to be very effective in achieving short start-up period. Therefore the steady state was achived after 4 weeks and 1 week based on T-COD and S-COD, respectively.