A galactooligosaccharide composition comprising a mixture of disaccharides, trisaccharides, a tetrasaccharide and a pentasaccharide for use in preventing or treating cognitive dysfunction and/or emotional disturbances in neuropsychiatric illnesses or ageing.包含雙醣、三醣、四醣及五醣之混合物之半乳寡醣組成物,用於預防或治療神經精神疾病或老化的認知功能障礙及/或情緒障礙之用途。