The diffusion coefficient of a solute particle within a membrane pore of comparable size is found to be less than its value in bulk solution. This hindered diffusion obviously depends on the sizes of solute and pore, and it is known both the solute concentration and the solution ionic strength are considerably influenced, although very little experimental data is available. In order to examine this fact, the diffusion coefficient of latex particle through the track-etched membranes with we11-defined cylindrical pore geometry has been measured by using diffusion cell apparatus. Note that both the relation of mass balance for the latex concentration and the principle of diffusional mass transfer across membranes are applied, which were provided in the previous studies, for the analysis of particle diffusion coefficient in the pore. Based on the Stokes-Einstein relation with virial type for the solute concentration, the bulk diffusion coefficient of latex for any KCl concentrations can be effectively estimated. The solute concentration dependence of hindered diffusion as a function of relative solute size has been observed, from which the hindered diffusion increases with increasing of solute concentration. This behavior suggests that, with increase of solute concentration, the repulsive interaction between a pore wall and a latex particle becomes strongly important than that of between pairs of latex particles. Therefore, as expected from the estimation of mass transfer coefficient, the particles are increasingly diffused firm bulk to pore region. Experimental results for latex concentration of 1 vol% showed that the hindered diffusion coefficient is decreased when the ionic strength of KCl is reduced ranging from 0.1 to 0.001 M. When the ionic strength decreases, the corresponding repulsion increment between a pore wall and a particle results in more restricted diffusion.