Asperginine (1), an alkaloid possessing a rare skeleton, was isolated from the cultural broth of the marine fungus Aspergillus sp. (Z-4) isolated from the gut of the marine isopod Ligia oceanica. The planar structure and relative configuration of 1 was determined by analysis of NMR and mass spectral data. Its absolute configuration was elucidated by Marfey's method, together with NOESY correlations of key hydrogen atoms. The cytotoxicity against prostate cancer PC3 and human HCT116 was assayed by the MTT method. Unfortunately, asperginine did not show any activity.