Cellulose acetate membranes with varied charge, hydrophobicity, porosity, and pore size have been developed by annealing, hydrolysis and oxidation of a basic cellulose acetate membrane. The effects of these modifications were characterized by poly(ethylene glycol) retention, contact angle and streaming potential measurements, and atomic force microscopy. The behavior of the membranes during humic acid adsorption experiments has also been studied. The results show that humic acid adsorption occurs both inside the pore and on the membrane surface. Experiments at different pH show the importance of solution properties on humic acid adsorption through modification of membrane and humic acid charge. Although many membrane characteristics are modified by hydrolysis and oxidation, neither treatment prevented humic acid adsorption on the CA membranes. The most effective surface treatment was with an anionic polymer, which significantly reduced adsorption of humic acid.