A new route was developed for preparation of cellulose acetate (CA) membrane from ramie fiber, a sustainable biomass. Sulfuric acid catalyzed acetylation of ramie fiber was carried out in acetic anhydride. The optimum reaction conditions were determined as ramie fiber to acetic anhydride ratio 1 : 6 (w/w), temperature 353 K, and reaction time 0.5 h. To prepare CA membranes with improved properties, CA was modified with polyethylene glycol (PEG 600, M-W = 600 g/mol(-1)) and tributyl citrate (TBC). The effects of CA content and additive concentrations given by a mixture design of experiments on CA membrane compaction, morphology, water flux, water content, and mechanical properties were studied. The thermal stability and hydrophobicity/hydrophilicity of membranes prepared with PEG 600 or TBC additives were also investigated. Addition of PEG 600 increased and addition of TBC decreased the thermal stability of CA membrane. The CA membranes prepared were used to separate dyes from their solutions. An inverse trend of the separation of solutions of Disperse Red S-R (DR) and Acid Scarlet 2G (AC) was observed for CA membranes modified with PEG 600 or TBC. The contact angle of CA membranes modified with PEG 600 or TBC decreased with increase in PEG 600 content, and increased with increase in TBC content. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 588-595, 2010