The present invention discloses a method for measuring the zeta potential at the cylinder's outer surface. In the measuring cell, the cylinder is held coaxially inside a reference tube and a given solution is forced to flow through the annular flow channel between the cylinder and the reference tube. The streaming potential induced by the flow forced with a hydraulic pressure drop is measured to determine the zeta potential, .zeta..sub.m, of the cylinder's outer surface by using the following Equation,.DELTA..times..times..mu..times..times..times..zeta..zeta..times- . ##EQU00001## where D is the permittivity, .zeta..sub.ref is the zeta potential of the reference tube, .mu. is the viscosity of the solution, k is the electric conductivity of the solution, and F is a correction factor for the electrokinetic model. Moreover, this invention also discloses a system for measuring the zeta potential of the cylinder's outer surface.