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.본 발명은 제2철 옥시수산화물과 안정하게 결합된 수소화 올리고당을 포함하는 개선된 안정성을 갖는 철 올리고당 화합물에 관한 것으로, 상기 수소화 올리고당 중의 이량체 당류의 함량은 수소화 올리고당의 총 중량에 대하여 2.9 중량% 이하이다. 추가적인 양태에서는 상기 화합물을 제조하는 방법을 제공할 뿐만 아니라 철 결핍성 빈혈증의 치료를 위한 조성물을 제조하기 위해 상기 화합물을 사용하는 것이 제공된다.
