The recoiling behavior of [Co(C2O4)3]3-, [Co(NO2)6]3-and [Co(CN)6]3-ions on in anion-exchanger was studied both by the dynamic and the static methods under various conditions. As the stability of the complex decreases, the separable yield increased as a general trend, and the effectiveness of the dynamic method in obtaining higher yield than the static method was clearly demonstrated.On the other hand, specific activity increased with increasing stability of the complex, i. e., with decreasing G values. The increase of pH generally decreased the separable yield and increased the specific activity. The effects of mesh size of resin and preirradiation by gamma rays were also studied. Since the observed tendency that the separable yield decreased with increasing stability constant of the complex ion seems to be a general one, a theoretical interpretation for this relationship was attempted.Extensive studies have been made of the recoil chemistry of cobalt complexes, possibly because of the availability of stable complexes of this element and of the ease in activating the element and in measuring its activity. One of the authors has recently introduced a "dynamic method" using a complex-loaded ion-exchanger, as a new technique for elucidating the recoil process as well as for enriching radioisotopes; and this method has an advantage in obtaining a yield higher than the usual static method in the cases of [Co(NH3)6]3+, [Co en3]3+,1) and [Cr(C2O4)3]3-ions.2)In this paper, a few anionic cobalt complex ions, [CO(C2O4)3]3 ,3)[Co(NO2)]3 ,4) and [Co-(CN)6]3-,5) were chosen as the target resin form, and the yield and specific activity of the separable fraction were estimated both by the dynamic and the static methods. Since it is already known that there are many factors affecting these quantities, this study was also performed under various experimental conditions: different irradiation positions in a reactor,1,6) different pH of the eluent,2,7) differing mesh size of resin,8) and pre-irradiation by gamma rays.6,9) The G values of the complexes adsorbed on the resin by gamma rays were also