In our study of antifungal compounds from marine invertebrates, we found significant activity against Candida albicans in the ethanol extract of an ascidian Didemnum sp. collected from the Great Barrier Reef, Australia. Here, we report the isolation and structure elucidation of the major antifungal compound (R)-(E)-l-aminotridec-5-en-2-ol (1), together with minor compounds 6 and 7 which were characterized as their N-Boc derivatives 3 and 4. The new compounds appear to be related to sphingosine, a widely distributed amphiphilic amino alcohol. In the agar plate disk diffusion assay, amino alcohol 1 trifluoroacetate showed moderate activity against Candida albicans (9-mm zone of inhibition at 50 pg/disk). The Boc derivatives 3 and 4 were hydrolyzed to give amino alcohols 6 and 7 with activity comparable to that of 1, while the free base of 1 showed slightly enhanced activity (11 mm at 50 pg/disk). The structures of compounds 1, 6, and 7 join an expanding family of modified marine sphinganoids, and the biosynthesis and mechanism of action of 1 warrant further investigation.