The aim of this experimental work was to evaluate the carbonaceous constituents in textile wastewater, and the infl uence of slowly biodegradable products, also to compare two processes: Membrane bioreactor (MBR) and activated sludge (AS) for treating textile wastewater. The MBR pilot plant includes an aerobic reactor of 50 l, and membranes of micro and ultra fi ltration, the AS pilot plant has an aerobic reactor of 4 l. The processes were run 3 times over 244 d, with the same relative F/M and SRT. Respirometry was carried out to fi nd the carbonaceous constituents in the wastewater, and also the Ultimate BOD, the mixed liquor suspended solids (MLSS) to evaluate the sludge, and different analysis: chemical oxygen demand and color removal, in order to evaluate process performance. The results show that the range of reduction of COD emissions using the MBR was 89–92%, and using AS was 54–70%, the color removal using MBR was 70% with MF membranes, and 72–73% with UF membranes, and 28% using AS. These results demonstrated that the textile wastewater could be treated by biological treatment but with high SRT, and also that the MBR is more effi cient and stable that a conventional activated sludge process for treating textile wastewater