Background Landfill leachate has been known as non-biodegradable/hardly-biodegradable wastewater, which contains significant amount of soluble organic and inorganic compounds. However, membrane bioreactor (MBR) technology have become a more viable treatment option for complex and recalcitrant compounds compared to activated sludge systems. Methods This study aims at evaluating the performance of anaerobic membrane bioreactor (AnMBR) for the treatment of middle/old-aged landfill leachate (LFL).AnMBR was operated at different hydraulic retention times (HRTs) (48-12 h) and relaxation and backwashing (30 min-5 min, 5 min-0.5 min) periods. Additionally, Air stripping (pH 8, 24 g lime/L, 1.4 L/s air flow rate) as a pretreatment was evaluated prior to AnMBR. Results Air stripping removed about 90%, 25%, and 64% NH4+, COD (Chemical Oxygen Demand) and color (RES620), respectively. The best results were obtained in combined air stripping-AnMBR operation corresponding to 95%, and 83% overall removals of color, and COD removals, respectively. Maximum methane yield and COD removal rate in AnMBR were 0.35 L methane/g COD (removed) and 5 gCOD removed /L.d, respectively. Conclusion Pretreatment provided higher AnMBR flux that reached to 5.5LMH but increased fouling frequency due to the calcium precipitates in AnMBR which was verified with SEM-EDX analysis. Additionally, DEHP and DINP were not detected in permeate indicating AnMBR was successful for removing these micropollutants. This study showed that pretreatment clearly increased methane yield and COD removal rate.