Seven new compounds, pleosporallins A-G (1-7), were isolated from Pleosporales sp., a fungus derived from a marine alga Enteromorpha clathrata. The structures of these compounds were elucidated by extensive analysis of NMR, MS, CD spectra and single crystal X-ray diffraction. Compounds 4 and 5 showed antimicrobial activity with their MIC values of 9.48 μg/ml and 7.44 μg/ml against Clavibacter michiganense subsp. Sepedonicus and Candida albicans, respectively. Compounds 1-3 exhibited moderate inhibitory activities against the lipopolysaccharide (LPS) induced intracellular IL-6 production of murine macrophage cell line RAW264.7.