A process for preparing low-viscosity water-soluble cellulose ethers by the oxidative decomposition of higher-viscosity cellulose ethers with hydrogen peroxide is described. The process involves: (a) forming, under conditions of intensive mixing and at temperatures of 65-125 C., a mixture of, (i) one or more higher-viscosity cellulose ethers, and (ii) an aqueous solution of hydrogen peroxide, the proportions of the mixture being selected in such a way that the hydrogen peroxide content is 0.1-10 wt. % in relation to the dry cellulose ether, the solids content of the mixture is at least 25 wt. % in relation to the total weight of the mixture; and (b) agitating continuously the mixture of step (a) at temperatures of 65-125 C. until at least approximately 90% of the hydrogen peroxide has been spent.