Tracer-diffusion coefficients of Co2+ ions have been determined in 1% agar gel containing transition metal chlorides, viz. ZnCl2, NiCl2 and MnCl2 over the concentration range of 10–6–0.15 M at 25°C using the zone-diffusion technique. The results are compared with calculated values on the basis of Onsager's theory and the deviations are accounted for on the basis of various types of interactions in the ion-gel water system. Further, activation energy for the tracer-diffusion of Co2+ ions in the above mentioned electrolytes has been obtained as a function of electrolyte concentration, using measurements in the temperature range of 25–50°C. The trend in activation energy is explained on the basis of the WANG's model.