Abstract: Both CSTR and batch mode were employed to investigate the variation of young and old landfill leachate characteristics during Fenton process.It was shown that ammonia-nitrogen,nitrate-nitrogen and chloride changed little after treatment.The fluoride concentration increased greatly and the removal of IC was very high during the process.COD and TOC decreased after Fenton process.Moreover,the percentage of COD and TOC removal from old leachate was slightly greater than that from young leachate.This was mainly due to the diferent HMWOM to LMWOM ratio in different landfill leachate.In addition,most of the removal efficiencies in this work were lower than those achieved in reference.