Xylanthraquinone (1), a new anthraquinone, along with three known compounds, altersolanol A (2), deoxybostrycin (3) and bostrycin (4) was isolated from the fungus Xylaria sp. 2508 from the South China Sea. The structures of these compounds were identified by NMR experiments, and the absolute configuration of compound 1 was further confirmed by single-crystal X-ray diffraction with Cu Kα radiation. Compounds 1-4 did not show inhibitory activities against Mycobacterium tuberculosis protein tyrosine phosphatase B (IC50 values more than 100 μM).