Abstract: The kinetics and mechanism of the extraction of Co(Ⅱ) from sulphate solution with HDEHP in 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 interface reactions:Co⁺⁺+2HA(i)=CoA₂(i)+2H⁺ CoA₂(i)+2H₂A₂(o)=CoA₂•2HA_(o)+2HA(i)where (O) and (i) represent organic phase and interface respectively. The influences of sulphate, chloride and nitrate concentration on the extraction rate were also discussed.