According to a process for production of alkylene oxide polymers offered by the present invention, an alkylene oxide is subjected to a polymerization reaction under presence of a catalyst in a solvent containing an aliphatic hydrocarbon having from five to seven carbon atoms and a branched structure. The aliphatic hydrocarbon is provided preferably by 2-methyl pentane, 3-methyl pentane, 2,3-dimethyl pentane, 2,4-dimethyl pentane, etc. The alkylene oxide is provided preferably by ethylene oxides and/or propylene oxides.