A new aromatic amine named pestalamine A (1), as well as a known diketopiperazine (2) and four known phenol or aromatic amine derivatives (3–6) were isolated from mangrove-derived endophytic fungus Pestalotiopsis vaccinii. The structure of pestalamine A (1) was determined by spectroscopic methods, especially 2D NMR analyses. Pestalamine A (1) showed moderate cytotoxicities against MCF-7, HeLa, and HepG2 human cancer cell lines with IC50 values of 40.3, 22.0, and 32.8 mM, respectively.