Reactive extraction of penicillin G at pH 5 and reextraction at pH 7-8 were performed using Amberlite LA-2 (carrier) in n-butyl acetate. The volume ratios of aqueous feed phase to organic extract phase in extraction and organic extract phase to aqueous strip phase in reextraction were varied, and the effects on the degree of extraction and enrichment were studied. The effects of initial concentration ratio of carrier to penicillin G were also investigated. It was found that there existed an optimum carrier concentration giving the maximum degree of extraction and enrichment. Procedure for the selection of volume ratios and concentration ratio at a desired degree of extraction and enrichment was described for initial penicillin G concentration of 10 mmol.dm-3, and generalized to be applicable for any concentrations of penicillin G. Finally, sodium carbonate solution was successfully applied as an aqueous strip phase on behalf of buffer solution in reextraction to avoid the disadvantages of using buffer solution and to shorten the reextraction time.