The invention relates to an oligosaccharide having a weight average molecular weight (Mw) of less than 3,000 Daltons, wherein said oligosaccharide comprises functional aldehyde groups and has a dimer saccharide content of 2.9 % by weight or less, based on the total weight of the hydrogenated oligosaccharide. The invention also relates to a process for preparing the oligosaccharide, which process comprises the steps of: hydrolysing a polysaccharide so as to reduce its molecular weight, wherein the resulting oligosaccharide comprises functional aldehyde groups, and fractioning the oligosaccharide according to molecular weight, so that the purified fraction has a weight average molecular weight equal to or less than 3,000 Daltons. The procedure of purification is performed 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.本発明は、鉄オキシ水酸化物と安定に会合する水素化オリゴ糖を含む改良された安定性を持つ鉄オリゴ糖化合物に係り、水素化オリゴ糖の総重量に基づき、上記水素化オリゴ糖中の二量体糖の含有量は2.9重量%以下である。更なる態様において、上記化合物の調製の方法ならびに鉄欠乏性貧血の治療のための組成物の調製のための上記化合物の使用を提供する。
