The purpose of this research was to isolate antimicrobial compounds from endophytic fungi isolated from Casearia grewiaefolia Vent., Picrasma javanica Bl., Oroxylum indicum (L.) Vent. and Erythrina variegate Linn. Crude extract of endophytic fungus isolate 10B was purified by chromatographic techniques to afford nine known compounds which were identified as alternariol monomethyl ether (1), 5-carbomethoxymethyl-2-heptyl-7-hydroxychromone (2), altersolanol A (3), macrosporin (4), 1, 2, 4, 5-tetrahydroxy-7-methoxy-2-methyl-1, 2, 3, 4-tetrahydroanthracene-9, 10- dione (5), alternariol (6), altenusin (7), 3’-methoxy-2-methylbiphenyl-4, 5, 5’-triol (8) and 5’- epialtenuene (9). The chemical structures of the isolated compounds were elucidated through extensive analyses of NMR and by comparison with literatures. Compound (3), (5) and (7) exhibited antibacterial activity by MIC assay. By checkerboard technique, compound (5) and compound (7) showed synergistic activity with tetracycline against S. aureus (FIC index 0.12) and with ceftriaxone against P. vulgaris (FIC index 0.09), respectively. Identification of fungus 10B based on conventional method and molecular method suggested that 10B was Alternaria sp.