Marianins A (1) and B (2), two new prenylated phenylpropanoids, were isolated from the culture extract of the fungus Mariannaea camptospora. Structures of marianins were elucidated by interpretation of NMR and other spectroscopic data. 1 is a 5-methylcoumarin bearing two prenyloxy groups, while 2 is an orcinol derivative substituted with a 3,3-dimethyl-4-pentenoyl chain. 2 is possibly derived from 1 through a Claisen rearrangement of the prenyl group, followed by lactone hydrolysis and decarboxylation. These compounds showed weak antibacterial activity against Micrococcus luteus.