Different amounts of (N,N＇-disalicylideneethylenediamin)cob alt (CoS) were blended to a cobalt (II)-neutralized sulfonated EPDM (Co-(II)-S-EPDM) ionomer membrane to enhance its oxygen-enriching ability. Various influence factors on permeabilities and selectivities of the composite membranes, such as the gas pressure difference, the CoS content, and the testing temperature have been investigated. Oxygen permeability coefficients (P-O2) and oxygen/nitrogen separation factors (alpha(O2/N2)) increased simultaneously by decreasing the gas pressure difference or by increasing the CoS content. In comparison with the EPDM matrix, P-O2 and alpha(O2/N2) of Co-(II)-S-EPDM-CoS (85/15) composite membrane increased from 11.0 Barrer and 4.38 to 37.0 Barrer and 9.60. Obvious enhancement in the oxygen-enriching property shows that the dual actions of cobaltous ion crosslinking and addition of an abundant cobalt complex may be an effective way to improve a rubbery polymer membrane. As high as 15 wt % of the CoS could be blended.