This research is aimed to suggest any possibilities of upgrading nitrogen and phosphorus removal in the exsisting activated sludge process with simple modification. The comparition between a partially aerated (A/O) and fully aerated activated sludge process was made at different mixing and aeration time, and sludge recycle to evaluate the effect of compartalized reaction tank on COD, nitrogen and phosphorus removal. The COD removal efficiency showed up to 95% in the A/O process as well as fully aerated activated sludge process. In the A/O process the substrate removal efficiency remained constant irrespective of anoxic/oxic reactor retention time ratios. Nitrogen and phosphorus removal efficiency in the A/O process was higher than that in the fully aerated activated sludge process. The efficiency in the A/O process was strongly affected by recycling rate. The total nitrogen removal efficiency increased with increasing recycle rate in the range of 25% to 200%. Phosphorus removal efficiency in this process trended to increase as the anoxic reactor volume in the system increased. Sludge settleability improved greatly as the first reactor volume to total reactor volume decreased.