A porous ion exchanger includes an open cell structure including interconnected macropores and mesopores whose average diameter is in a range of 1 to 1000 .mu.m existing on walls of the macropores. Moreover, a total pore volume is in a range of 1 to 50 ml/g, ion exchange groups are uniformly distributed, and an ion exchange capacity is not less than 0.5 mg equivalent/g of dry porous ion exchanger. The porous ion exchanger can be used as an ion exchanger filled into a deionization module of an electrodeionization water purification device, solid acid catalyst, adsorbent, and filler for chromatography.