This study reports the isolation and characterization of six novel tetrahydroxanthone derivatives, paraconixanthones A - F (1-6), a new diphenyl ether (7), and thirteen known compounds (8-20) from the endophytic fungus Paraconiothyrium sp. AC31. The chemical structures were elucidated using NMR, MS, X-ray diffraction, and ECD analyses. Paraconixanthones A and B (1 and 2) represent the first examples of tetrahydroxanthone-benzoate dimers, suggesting a unique biosynthetic pathway. Compound 12 exhibited potent anti-proliferative activity against HepG2 hepatocellular carcinoma cells (IC