A new type of charge-mosaic membrane was prepared from poly(4-vinyl pyridine) microspheres 250-350 nm in diameter as an anion-exchange element and from linear poly(sodium styrene sulfonic acid) as a cation-exchange element. The mosaic structure on the surface of the membrane and the continuous connection of the microspheres in the membrane were confirmed by scanning electron microscopy observations and the electrical conductivity of the membrane. The microspheres were continuously connected from one side to the other side of the membrane surface when the weight fraction of the microspheres increased more than 20-25 wt % in the membrane. The flux of KCl, the permeability coefficient of KCl, the volume flux, and the selectivity dialysis separation of the electrolyte (KCl) and nonelectrolyte (glucose and saccharose) of the membrane indicated that it had the characteristic properties of a charge-mosaic membrane. Ion-exchange membranes composed of each raw material of the charge-mosaic membrane did not show these properties. (C) 2003 Wiley Periodicals, Inc.