Disclosed herein is an iron oligosaccharide compound comprising a hydrogenated oligosaccharide in stable association with ferric oxyhydroxide, the hydrogenated oligosaccharide having a weight average molecular weight (Mw) of less than 3,000 Daltons, characterized in that the content of dimer saccharide in said hydrogenated oligosaccharide is 2.9 % by weight or less, based on the total weight of the hydrogenated oligosaccharide. Also disclosed is a process for preparing said compound comprising the steps of: hydrolysing a polysaccharide so as to reduce its molecular weight, hydrogenating the resulting oligosaccharide to convert functional aldehyde groups into alcohol groups, fractioning the hydrogenated oligosaccharide according to molecular weight, so that the purified fraction has a weight average molecular weight equal to or less than 3,000 Daltons, combining the resultant fractionated hydrogenated oligosaccharide as an aqueous solution with at least one water-soluble ferric salt, adding base to the resulting aqueous solution to form ferric hydroxide, and heating the resultant basic solution to transform the ferric hydroxide into ferric oxyhydroxide in association with said oligosaccharide； characterized in that step (c) comprises a procedure of purification by one or more membrane processes having a cut-off value between 340 and 800 Daltons, which procedure is continued until the content of dimer saccharide in the purified fraction of oligosaccharide has been reduced to 2.9 % by weight or less, based on the total weight of the hydrogenated oligosaccharide.
