The kinetics and mechanism of the extraction of Co(Ⅱ) from sulphate solution withHDEHPin kerosene were studied by means of single drop method at 25℃, The experi-mental results indicate that the extraction process is controlled by the following interfacereactions: Co~(++)+2HA(i)=CoA_2(i)+2H~+ CoA_2(i)+2H_2A(_2(o))=CoA_2·2HA_(o)+2HA(i)where (O) and (i) represent organic phase and interface respectively. The influencesof sulphate, chloride and nitrate concentration on the extraction rate were also discussed.