The municipal landfill leachate was treated in a hydrolysis–acidification reactor (HAR)/aerobic bio-contact oxidation reactor (ABOR) following a pretreatment with ultrafiltration (UF) membrane. Experiments were conducted continuously for 44 days at a constant flow rate of 20ld −1 and organic loading rates (OLRs) from 0.75 to 1.5kgCODm −3 per day. The results showed that COD of the leachate steadily decreased from 20,015mgl −1 to less than 3000mgl −1 , and NH 4 -N decreased from 368.6mgl −1 to 259.3mgl −1 in the UF process. The COD and NH 4 -N removal efficiency of HAR was 56.7% and 27.7%, and that of ABOR was 94.6% and 86.7%, respectively. The total COD and NH 4 -N removal efficiency reached 99.6% and 93.2%, respectively. UF and HAR played a critical role in raising the biodegradability of the landfill leachate, while ABOR had an important function on removing the dissolved NH 4 -N in leachate.