Marine-derived fungi have attracted increasing attention from those seeking new pharmaceutically useful natural products in recent years[1].Three new dihydroisocoumarin penicimarins G-I (1-3),together with one known dihydroisocoumarin (4) were obtained from a fungus Penicillium citrinum isolated from the mangrove Brguiera sexangula var.rhynchopetala collected in the South China Sea.Their structures were elucidated by the detailed analysis of comprehensive spectroscopic data.The absolute configuration of 1 was determined by the X-ray diffraction analysis using Cu Kα radiation.The absolute configurations of 2-3 were determined by comparison of their CD spectra with the literature.All compounds were evaluated for their antibacterial activities and cytotoxic activities.