Charged UF/NF membranes have been developed by phase inversion. The membranes were prepared with polyetherimide (PEI) and sulfonated poly(ether ether ketone) (SPEEK). SPEEK was used to improve the hydrophilic properties and permeability of the PEI membrane, as well as to provide surface charges. The membrane properties were reproducible when the proportions of SPEEK were similar to 3.0% and similar to 6.0% in the total blend of polymers. With the increase of SPEEK from 3% to 6% in the casting solution, water permeability increased from 24.0 +/-2.1 x 10(-11) to 36.6 +/- 3.0 x 10(-11) m(3) s(-1) N-1, rejection of sodium chloride and PEG 1500 increased from 0.399 to 0.599, and 0.600 to 0.93 1, respectively (as measured at 100 kN m(-2)). SEM cross-sectional images showed a top layer with a sponge-type structure and a support layer with a finger-like structure. With the addition of tetrahydrofuran (THF) and 1,4-dioxane to the casting solution, water permeability decreased, rejection of PEG 1500 decreased and rejection of NaCl was generally little changed. (c) 2004 Elsevier B.V. All rights reserved.