Abstract: A new alkaloid (1) and six known compounds (2-7) were isolated from the solid fermentation extract of the endophytic fungus Alternaria tenuissima Pas85 of Phragmites australis by silica gel column chromatography, Sephadex LH-20 column chromatography, high performance liquid chromatography and other chromatographic techniques. The structures of these compounds were determined by HREIMS, NMR, IR spectroscopy, and literature comparison, and the anti MRSA (methicillin-resistant Staphylococcus aureus) activity of 1-5 were tested. Compounds 1, 2, 3 and 4 exhibited certain inhibitory activity with MIC values of 64, 4, 32 and 32 μg·mL^-1, respectively, and compound 5 showed no significant inhibitory activity.