The concentration dependence of the kinetics and equilibrium characteristics for the exchange of cesium ions on cobalt hexacyanocobaltate(III) has been studied. It is found that the rate of cesium sorption increases with decreasing cesium concentration in solution. The exchange reaction proceeds via two stages, the first stage is rather fast followed by a much slower one. The equilibrium characteristics of the distribution coefficients for cesium are interpreted in terms of the Langmuir-Hückel isotherm. The heat of sorption and activation energy are determined from the temperature dependence of the exchange reaction.