This study investigated antibacterial compounds from the rice medium of the tilapia intestinal derived fungus Alternaria tenuissima SCSIO41701.The compounds were separated by silica gel column chromatography,HPLC and other chromatographic techniques.The structures of the compounds were identified by 1H NMR,13C NMR,and comparison with the NMR data of literatures.Totally,nine compounds were isolated from the antibacterial fractions of the tilapia intestines derived fungus Alternaria tenuissma.These compounds were identified as aternariol (1),aternariol methyl ether (2),3-hydroxyalternariol 5-O-methylether (3),(-)-altenuene (4),(+)-isoaltenuene (5),altenusin derivative (6),alternariphent (7),talaroflavonene (8),and alternarienonic acid B (9).Only compound 1 showed obvious inhibition activity against the growths of Streptococcus iniae and S. agalactiae at 25 μg/dics with inhibition zones of 10 mm,and its MIC values were 12.5 μg/mL.