Background: Wastewater collection, treatment, discharge, additionally as reusing the treated wastewater in urban are critical factors for maintaining public health preventing contamination of water resources. This study aimed to investigate the performance of enhanced modified Ludzack Ettinger process-oxic settling anaerobic (MLE-OSA) process for treating real municipal wastewater in Sari wastewater Treatment, Sari City, Iran. Methods: To combine the OSA process technique with the MLE system, the Sludge Holding Tanks (SHT) were implemented in the return sludge line of designed pilot studies which comprised 1) MLE, which was regarded as the control system similar,2) MLE-OSA4 with a 70-L SHT operated at 4-h Hydraulic Retention Time (HRT), and 3) MLEOSA6 with a 107-L SHT operated at 6-h HRT. To start the process, the overflow effluent of the primary settling tank of the Sari wastewater treatment plant was used. After 45-60 days, the reactors reached a steady state. The parameters of Dissolved Oxygen (DO), Oxidation-Reduction Potential (ORP), temperature, pH, Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5), Total Suspended Solids (TSS), and nutrients were analyzed. Results: The results revealed that the average TSS, COD, BOD, phosphorus, nitrite, nitrate, and total nitrogen in MLEOSA4 effluent decreased 20. 1, 14. 6, 2. 97, 10, 51. 1, 19. 3, and 20. 7%, respectively compared to MLE. Similarly, in MLE-OSA6, the values decreased 34. 2, 16. 1, 14. 6, 16. 7, 69. 6, 31. 3, and 25. 8%, respectively compared to the control process. Conclusion: Therefore, using natural wastewater, the enhanced MLE-OSA process showed better performance in removing the study parameters and better quality for the effluent. Furthermore, the quality of effluent is following the Iran Department of Environment (IDE).