Landfill leachate of Hong Kong was first treated by the upflow anaerobic sludge blanket (UASB) process. At 37 degrees C, pH 7.1-8.5 and a HRT of 5.1-6.6 days, the process removed 66-90% of COD in the leachate for loading rates of 1-2.4 g-COD/l day depending on the strength of landfill leachate. The final effluent contained 1440-1910 mg-COD/l and 70-91 mg-BOD/l. About 92.5% of the total COD removed was converted to methane and the rest was converted to biomass with an average net growth yield of 0.053 g-VSS/g-COD-removed. The granules developed in the UASB reactor were 0.5-1.5 mm in size and exhibited good settleability. The UASB effluent was then further polished by two oxidation processes. The UASB-ozonation process removed 93.0% of the 12900 mg/l of COD from the raw leachate. The UASB-Fenton-ozonation process improved the COD removal efficiency to 99.3%. The final effluent had only 85 mg/l of COD and 10 mg/l of BOD5. Ozonation was most effectively conducted at pH 7-8 with the addition of 300 mg/l of H2O2 and for the duration of 30 min. Ozonation also significantly improved the biodegradability of the organic residues. Nearly 50% of these residues could be used as carbon source in denitrification.