The ascomycete Dichotomomyces cejpii was isolated from the marine sponge Callyspongia cf. C. flammea. Three new steroids (1–3), two of which are present as glycosides, with an untypical pattern of carbon–carbon double bounds, were obtained from fungal extracts, as well as the known xanthocillin X dimethyl ether (4). Compounds 2 and 4 were evaluated in an Alzheimer's disease cellular assay and found capable of preventing the enhanced production of amyloid β-42 in Aftin-5 treated cells. Aβ-42 lowering agents are considered as candidates for the treatment of neurodegenerative Alzheimer's disease.