Abstract: The treatment of landfill leachate from a garbage landfill in Shanghai by Fenton oxidation process was studied. The humic acid and fulvic acid were extracted and isolated from the landfill leachate before and after the treatment by Fenton oxidation. Gel filtration chromatography and three-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM) were applied to analyze the molecular weight (MW) distribution and the fluorescence characterization of organic compounds in the landfill leachate before and after the treatment by Fenton oxidation. The results showed that the ρ(BOD₅)/ρ(COD_Cr) ratio of the landfill leachate could be enhanced from 0.011 to 0.285 by Fenton oxidation. The results of the molecular weight (MW) distribution and the fluorescence characterization showed that the increase of the biodegradability of the landfill leachate could be due to the decrease of the MW distribution of organic matter in the landfill leachate, especially the removal of the high MW humic acid and the decrease of MW of the fulvic acid.