The performance of an aerated submerged fixed film reactor (ASFFR) in upgrading process of Parkandabad wastewater treatment plant (WWTP) was studied in a pilot plant. The experiments were performed at hydraulic retention times (HRTs) of 6, 12, 18 and 24 h (based on empty reactor volume) and the performance of the ASFFR was evaluated based on the removal of organic matter (BOD5 and COD), SS, and NH4+-N The average BOD5 /m3 and COD removal efficiencies were in the ranges of 83.0-92.2 % and 80.7-90.7 %, respectively, depending on HRT. The relationship between the organic loading rate and organic removal rate was linear and the maximum organic removal rate was obtained as 1.74 kg BOD5/m3.d which was at organic loading rate of 2.10 kg BOD5 /m3.d. The average SS removal efficiencies at HRTs of 6, 12, 18 and 24 h were obtained to be 81.8, 83.4, 82.0 and 87.1 %, respectively. The ammonia nitrogen removal efficiency increased slightly as the HRT increased. Therefore, by increasing HRT from 6 to 24 h, the average NH4+-N removal efficiency increased from 53.7 to 63.3 %. Also the NH4+-N removal rate was as a linear function of the NH4+-N loading rate within the range of loading rates studied. The results indicated that the reactor was a feasible alternative for the upgrading of Parkandabad WWTP.