The interfacial electrokinetic potentials were measured by streaming potential method which was generally used in the electrochemical study of interface of fiber and dye solution. The results were transformed into ζ potential by Helmholtz-Smoluchowski formular, into surface charge density by Suzawa formular and into surface dye adsorption of fibers. The ζ potential of wool or acrylic fiber in dye mixture solution showed similar trend as was found in single dye solution, but the total dye up-take of wool fiber increased at higher pH value. It is postulated that the increase in dyeing sites by the dissociation of carboxyl groups of wool fiber at higher pH is responsible for the increased dye up-take.