An extract from leaves of mulberry is disclosed. The extract has an IC50 value sufficient to inhibit α-glucosidase I. The extract may comprise 5-40% (w/w) total imino sugars and 20-70% (w/w) total amino acids. The extract may reduce the production of melanin for the treatment of such ailments or diseases caused by pigmentation as freckle, chloasma, striae gravidarum, sensile plaque and melanoma. The extract may also control blood glucose level.