This paper describes an ultraprecision ELID (Electrolytic In-Process Dressing) grinding method of fused silica and single crystal silicon X-ray mirrors with a large ultraprecision aspheric grinding system, and the grinding characteristics. The X-ray mirrors materials was ground with the grinding system by ELID-grinding using #325, #1200 and #4000 cast iron-cobalt hybrid bonded diamond wheels, and the grinding characteristics of this X-ray mirror were investigated. The results, very good ground surface of Ra 8.7nm and Ry 97nm of 300mm mirror can be achieved.
