This paper discusses combustion control using fuzzy logic for a sewage sludge melting furnace. The sewage sludge melting process is gaining attention as an effective method for reducing sludge volume. The slag from molten sludge is stable, causes no pollution, and can be used as a by-product. However, the operation of a sludge melting plant requires expert operators who have to deal with complex phenomena that take place in a melting furnace. In an effort to facilitate the operation, the authors have employed a control system which features the use of fuzzy logic for automatic combustion control in a cyclone type sewage sludge melting furnace. Confirmation was made that this fuzzy logic combustion control system functioned effectively for controlling the furnace temperature, O2 concentration in the furnace outlet flue gas, and concentration of NOx.