<jats:p> Six metabolites (1–6), including 1 new fusaric acid derivative, designated atransfusarin (1), and 5 known compounds, (3 R,6 R)-3-benzyl-6-isopropyl-4-methylmorpholine-2,5-dione (2), daucoterol (3), adenosine (4), cerebroside B (5), and 2,3-dihydroxypropyl ( Z,Z)-9,12-octadecadienate (6), were isolated from the solid culture of an endophytic Alternaria atrans MP-7, associated with the medicinal plant Psidium guajava. The structure of the new compound was elucidated by spectral data. The antifungal test indicated that (3 R,6 R)-3-benzyl-6-isopropyl-4-methylmorpholine-2,5-dione (2) showed obvious inhibitory activity against Alternaria solani, Colletotrichum gloeosporioides, and Phyricularia grisea. Compared to fusaric acid (1a), even though the antifungal activity of atransfusarin (1) against A. solani, C. gloeosporioides, and P. grisea was greatly decreased, its inhibitory effect against Botrytis cinerea was still retained.