Whey is the main byproduct obtained from cheese production, and it contains a high concentration of valuable organic matter, but demineralization is needed before it can be used. Nanofiltration (NF) membranes have high permeability for monovalent salts (e.g. NaCl, KCl) and organic compounds with low molecular weight, and very low permeability for organic compounds of molecular weight higher than 300 Da, so it is a good alternative for simultaneous concentration and demineralization of whey. In this paper, whey was acidified at different pH to measure the desalination. The results indicated that the best condition for demineralization was at the isoelectric point of whey (pH = 4.60). On the other hand, when the pH was at the isoelectric point of beta-lactoglobulin (5.18, the main protein of whey), a good effect of demineralization could be obtained as well, and when diafiltration was applied, the demineralization effect was even higher at the pH of 4.60, and the demineralization rate was 72%. (c) 2010 Elsevier B.V. All rights reserved.