Biodegradability enhancement of landfill leachate using air stripping followed by coagulation/ultrafiltration (UF) processes was introduced. The air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen (NH(4)-N) at air-to-liquid ratio of 3500 (pH 11) for stripping 18 h. The single coagulation process increased BOD/COD ratio by 0.089 with the FeCl(3) dosage of 570 mg l(-1) at pH 7.0, and the single UF process increased the BOD/COD ratio to 0.311 from 0.049. However, the combined process of coagulation/UF increased the BOD/COD ratio from 0.049 to 0.43, and the final biological oxygen demand (BOD), chemical oxygen demand (COD), NH4-N and colour of leachate were 1223.6 mg l(-1), 2845.5 mg l(-1), 145.1 mg l(-1) and 2056.8, respectively, when 3 kDa molecular weight cut-off (MWCO) membrane was used at the operating pressure 0.7 MPa. In ultrafiltration process, the average solution flux (J(V)), concentration multiple (M(C)) and retention rate (R) for COD was 107.31 m(-2) h(-1), 6.3% and 84.2%, respectively. Crown Copyright (C) 2009 Published by Elsevier B.V, on behalf of The Institution of Chemical Engineers. All rights reserved.