To provide a process for producing a polyether, which comprises subjecting an alkylene oxide and the like to ring-opening addition polymerization to an initiator in the presence of a double metal cyanide complex catalyst (DMC catalyst), which can be carried out by use of a DMC catalyst at a low concentration, and accordingly the amount of the DMC catalyst remaining in a polyether to be obtained can be reduced.A process for producing a polyether, which comprises subjecting an alkylene oxide and an oxygen-containing heterocyclic compound other than an alkylene oxide, to ring-opening addition polymerization to an initiator having a hydroxy group in the presence of a DMC catalyst, wherein prior to the ring-opening addition polymerization, the DMC catalyst and the initiator are subjected to mixing treatment at a temperature of from 125° C. to 180° C. under an absolute pressure of at most 0.06 MPa for from 10 minutes to 24 hours.