To obtain an ion-exchange membrane having a composite reinforcing woven fabric composed of a reinforcing yarn forming a leno-woven structure and a sacrifice yarn forming a plane-woven structure, having high numerical aperture, and resistance to cross-displacement advantageous in weaving of the reinforcing woven fabric and production of the ion-exchange membrane, and capable of exhibiting the effect of the sacrifice yarn contributing to the reduction of membrane resistance.

This ion exchange membrane having reinforcing yarns forming a leno-woven structure, and sacrifice yarns forming a plane woven structure is obtained. Preferably, the reinforcing yarn has 50-200 de size and composed of a perfluoropolymer, and the sacrifice yarn has 20-50 de size and composed of a polyethylene terephthalate, a rayon or a cellulose. The thickness of the warp yarn of the reinforcing yarn is preferably 1/2 of that of the weft yarn in denier. Both of the twist counts of the warp and weft yarns of the sacrifice yarn are each preferably 0-350 turn/m. The thickness of the composite reinforcing woven fabric is preferably 30-80 μm. A method for continuously passing the woven fabric through between heated rolls at ≥200°C and rolling the fabric while applying a tension to the fabric in the warp direction of the woven fabric is preferably used for the smoothening of the woven fabric.