A counteracting chromatographic electrophoresis (CAGE) separation device has been successfully built and tested. Experiments are performed with protein mixtures of BSA, Hg, Mg and Cyto-c to study the separation performances, concentration profiles, start-up methodology as well as influences of pH and ionic strength on the separation process. Mathematical models based on the fluid dynamics of the porous medium are proposed. Experiments indicate that the CAGE process has a good commercial potential in protein engineering and fine chemicals purification.