A new cyclic pentadepsipeptide, sansalvamide (1), has been isolated from organic extracts of the mycelium of a fungus of the genus Fusarium collected from the surface of the seagrass Halodule wrightii. The structure of 1 was determined through extensive analysis of 1D and 2D NMR data. Sansalvamide exhibited selective in vitro cytotoxicity toward COLO 205 colon and SK-MEL-2 melanoma cancer cell lines.