A new sesquiterpene, gxsespene A (1), and four known sesquiterpene derivatives 2-5 were isolated from the mangrove endophytic fungus Aspergillus sp. GXNU-MA1. Their structures were elucidated based on high-resolution electrospray ionization mass spectroscopy (HR-ESI-MS) datum, extensive nuclear magnetic resonance (NMR) spectroscopic analysis, and comparison with literature data. The structure of 1 was further confirmed by single-crystal X-ray diffraction analysis, and the absolute configuration of 1 was established. Compounds 1-5 were evaluated for their anti-inflammatory activities against the nitric oxide (NO) production, and compounds 1-5 showed moderate inhibitory activities with IC50 values ranging from 16.15 to 27.08 µM.