Landfills produce leachate which are very rich in organic and mineral matters. Their discharge in the natural environment necessarily requires a preliminary treatment stage, which can be very complex since thier qualities and quantities vary. A treatment line has been designed in accordance with the very strict quality norms, laid down by present regulations. It is made up of a membrane bioreactor and a reverse osmosis unit. The results show that the membrane bioreactor allows the treatment of ammonia and part of the COD, with a limited production of sludges, and that it produces an effluent suitable for the reverse osmosis.