The ion exchange between cobalt(Ⅱ)-form ion exchanger and calcium chloride solulion was studied by using a three-necked flask as the reaction vessel and the rate of exchange was measured by the colorimetric method.The influence of concentration of the calcium chloride solution on the mechanism of diffusion and the rate of exchange was studied.As the concentration of the calcium chloride solution was increased, the mechanism of diffusion changed from film diffusion (prevailing at and below 0.02 N), through mixed diffusion, to particle diffusion (prevailing at and above 0.1 N),the rate of exchange increasing gradually with concentration and finally reaching a limiting value.The particle diffusion constant, B, and the film diffusion constant, R, which characterized the exchange rate were calculated.Both from the theoretical discussion and from the experimental results, the method we used is simple and convenient and is sufficiently accurate for the study of the ion exchange kinetics.