The possibility of ethane/ethylene mixture separation at the passing these gases through polyethylene-graft-sulfonated polystyrene membranes in silver and hydrogen forms has been shown. The results showed that the permeability of ethylene and the value of the separation coefficient increased significantly with increasing relative humidity of the separated gases. It was concluded that in both cases the transfer of ethylene occured in the form of a positively charged complex. The patterns of change in the permeability and separation factor were explained on the basis of the structure of the initial membranes and the solubility of the separated gases in the "phases" forming the membrane.