A process for purifying a crude polyether, comprising contacting a crude polyether obtained by addition polymerizing an active hydrogen-containing compound with an alkylene oxide compound in the presence of an alkali metal-containing basic catalyst to an adsorbent comprising a synthesized hydrous magnesium silicate compound which satisfies the following requirements (1) to (5) in order to reduce the alkali metal content of the crude polyether: (1) it is represented by the following formula I: (CaO).sub.x.(MgO).sub.y.(Al.sub.2O.sub.3).sub.z.SiO.sub.2.mH.sub.2OI wherein x, y, z and m satisfy the following ranges: x