Experimental and theoretical studies on simultaneous extractive removal and stripping of penicillin G using two large-scale hollow fiber membrane contactors are performed. The influence of main concentration parameters (penicillin in the aqueous phase and amine-extractant in the organic phase) on the kinetics of the complex mass-transfer process (extraction/stripping) is examined. A mass-transfer model is developed in which both diffusional processes and chemical reactions in the extraction and stripping modules are taking into consideration. The individual and overall mass-transfer coefficients in both modules are determined and compared. The overall mass-transfer coefficient K F in the extraction module is found to be an order of magnitude higher than the corresponding value K R in the stripping module. The rate-controlling step(s) in each module separately and in combination are identified. It is shown that the simultaneous extraction/stripping is limited by the rate of the reverse chemical reaction (at higher penicillin concentration and lower amine concentration) or by the diffusion of the complex through the membrane in the second module (at higher carrier concentration), or combination of both rates of chemical reaction and membrane diffusion. The fractional diffusional resistances of the penicillin/extractant complex in the bulk organic solution are relatively small at all the conditions examined and in both modules. Conclusions are drawn how this process could be optimized.