Amamine (1), a new isoquinoline alkaloid, was isolated from the culture extract of an actinomycete Kitasatospora sp. HGTA304. The structure of 1 was determined by NMR and MS analyses in combination with UV data. Compound 1 displayed & alpha;-glucosidase inhibitory potential (IC50 value of 56 & mu;M) compared with acarbose (IC50 value of 549 & mu;M) as standard.