Ethyl tert-butyl ether (ETBE) is a fuel octane enhancer considered as a major bio-fuel in Europe. Blended with gasoline fuels, ETBE improves fuel combustion and reduces toxic hydrocarbon emissions. ETBE industrial synthesis leads to an azeotropic mixture EtOH/ETBE (20/80 wt%), which cannot be separated by simple distillation. According to former works, cellulose acetate (CA) membranes were extremely selective with a permeate EtOH content of 100% but their flux was too low for ETBE purification by the pervaporation (PV) membrane process. The affinity of the bio-based polylactide (PLA) for ethanol has also been reported for poly(vinyl pyrrolidone)/PLA blends for this application. In this work, new bio-based membranes were obtained by grafting CA with controlled PLA amounts by a "grafting onto" strategy. The CA-g-PLA copolymers were characterized by ATR-FTIR, H-1 NMR, DSC and SAXS. Their membrane properties were investigated in terms of structure-morphology-property relationships for the sorption and pervaporation of the targeted EtOH/ETBE mixture. PLA grafting onto CA strongly improved the flux (x12) while the ethanol permeate content remained in the very high range (C' > 90 wt%) for ETBE purification by pervaporation.