Saltwater culture of Myrothecium verrucaria, separated from a Spongia sp. collected in Hawaii, was a source of three new trichothecenes, 3-hydroxyroridin E (1a), 13'-acetyltrichoverrin B (2), and miophytocen C (3) and nine known related compounds (1b, 4, 5, 6, 7a, 7b, 8, 9a, and 9b). The stereostructures of the new compounds were established on the basis of 1D and 2D NMR spectral analyses and a chemical transformation. At the same time, the stereostructures of known compounds, 1b, 4, and 5 reported previously were also elucidated. All the compounds except 3 showed significant cytotoxicity against murine and human tumor cell lines. Moreover, the structure-activity relationships (SARs) were established from the results of the bioassay data.