The oxygen permeated through the film made by a polyurethane (PU) ionomer is demonstrated to be a siloxane-based polyurethane ionomer by infrared spectra. For siloxane-based polyurethane ionomer molecules in an aqueous solution, the surface tension was found to decrease slightly with an increase in the concentration of dimethyldichlorosilane (DMDCS) but to increase slightly with an increase in the ratio of NCO to OH. Owing to the increased phase volume of siloxane-based polyurethane ionomer molecules resulting from the hydrogen bonding effect and/or intermolecular interaction in the aqueous solution, the number-average particle sizes of these ionomer molecules increase considerably with an increase in the DMDCS concentration and the NCO/OH ratio, respectively. More importantly, the volume of the oxygen permeated through the film was found to be larger for the film made by the PU ionomer molecule with 0.02% (by weight) DMDCS than for the film made by the PU ionomer molecule without DMDCS. Our experimental results also suggest that the use of DMDCS in preparing siloxane-based polyurethane ionomers does substantially raise the amount of oxygen diffusing into the film made by these ionomer molecules.