From the red alga Caloglossa leprieurii, which was collected from the Xisha Islands in the South China Sea, a white crystalline compound was isolated. The compound was identified as the known modified dipeptide, aurantiamide acetate by MS and NMR. The structure of aurantiamide acetate was determined by two _ dimensional NMR spectroscopy for the first time. All the 1H and 13C NMR data were assigned unambiguously. The absolute configuration of aurantiamide acetate from marine organism was also confirmed.