The subject matter of the present invention is a method of manufacturing an aldose or an aldose derivative containing n carbon atoms on the hydrocarbonic chain, characterized by the fact that, in an aqueous phase, at least one acid derivative of saccharide with n+1 carbon atoms containing at least one .alpha.-hydroxy acid unit, and/or at least one salt of such an acid derivative of saccharide, is brought into contact with hydrogen peroxide in the presence of a quantity of at least one tungsten or molybdenum salt, said quantity being less than 4 equivalents, preferably less than 2 equivalents, expressed as the total number of moles of tungsten and molybdenum divided by the total number of moles of acid derivative(s) of saccharide and of salt(s) of acid derivative(s) of saccharide.