The objective of this study was to investigate the rejection of steroid hormone estrone by NF membranes as a function of feed water chemistry. Experimental results indicated that estrone rejection by NF membranes in electrolyte background solution decreased continuously during first 10h and then stabilized. A clear pH-dependency was observed for estrone rejection. DL membrane exhibited a better performance in terms of estrone rejection at pH 10.4 because the electrostatic repulsion between the dissociated estrone molecules and highly negative-charged DL membrane reduced the proximity of estrone to the membrane surface. The presence of HA in feed solution appeared to improve both of estrone adsorption on membrane and estrone rejection. The lower the solution pH value, the higher amount of HA adsorbed on DL membrane and the greater the increment in adsorption of estrone on membrane by addition of HA. More importantly, it was found that, the presence of HA could enhance the rejection of estrone under all the pH conditions investigated in this study, with the greatest "enhancement effect" on estrone rejection at pH4. (c) 2007 Elsevier B.V. All rights reserved.