Endophytes are bacteria or fungi that live in the intercellular spaces of the tissues of host plants without causing discernible manifestation of disease. Recently, endophytes have been recognized as important sources of a variety of structurally novel and biologically active secondary metabolites, including terpenoids, steroids, alkaloids, and isocoumarin derivatives. In the course of our search for new biologically active secondary metabolites from endophytic microorganisms residing in Maytenus hookeri (Celastraceae), we studied chemical substances from an endophytic fungus Alternaria alternata of Maytenus hookeri and isolated and characterized nine compounds, alternariol (1), alternariol monomethyl ether (2), 5-epialtenuene (3), altenuene (4), uridine (5), adenosine (6), ACTG toxin-E (7), ergosta-4,6,8,22-tetraen-3-one (8), and ergosta-7,24(28)-dien-3-ol (9) from the ethyl acetate–methanol–acetic acid extract of the solid-state fermentations of this fungus. Among them, compounds 5 and 6 were isolated for the first time from this genus Alternaria, both 8 and 9 first being obtained from the species. In this paper, we describe the isolation and structure elucidation of these compounds 1–9.