A new operational support system for high nitrogen removal in the batch type activated sludge process using intermittent aeration has been developed. The system consists of: (i) the index to change the intermittent aeration pattern and (ii) the menu in which several patterns are lined up in the order of total aeration time. If the index becomes out of predetermined range, the system suggests to the operator exchanging the pattern being used for a next upper or lower one. The analysis of the nitrification and denitrification in the batch type activated sludge process using mathematical models lead to the validity to use the ratio of aerobic to anaerobic duration time as the index, and its optimum value was found to be around 1.The index is obtained from the output of a DO meter without complex calculation. The systemshows high nitrogen removal because the balance of nitrification and denitrification is optimizedby keeping the ratio of aerobic to anaerobic duration time around 1, and it has a very practicable advantage because of its simplicity. A laboratory experiment applying the system resulted in good nitrogen removal, indicating the reliability of the system.