Purification of landfill leachates is a difficult question for which there is no general answer due to their diversity and possible evolution with time. The aim of this work was to characterize the landfill leachate considered and then to propose an efficient treatment for this effluent. The leachate analysis led us to consider a membrane separation process, namely ultrafiltration. The separation power was studied under several conditions. The results obtained show that purification is successful and we report the differences encountered using different membranes and modules. The best results at lab-scale were performed again using bench-scale modules and finally this study makes it possible to define an efficient process for which the type of membrane, its cutoff, the experimental, and backwash conditions are determined. Good experimental conditions are quite flexible. The design of an industrial plant can be deduced, which no doubt ensures a good purification (i.e., a high chemical oxygen demand retention).