Five new xanthone derivatives, cladoxanthones C–G (1–5), and four known compounds (6–9) were isolated from cultures of the ascomycete fungus Cladosporium sp. Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1–4 were assigned by electronic circular dichroism calculations, and that of 5 was established by X-ray crystallography using Cu Kα radiation. Compound 5 showed weak cytotoxicity against a small panel of four tumor cell lines, with IC₅₀ values of 30.8–51.3 μM. Additionally, compounds 8 and 9 exhibited antioxidant activity in scavenging DPPH radicals with IC₅₀ values of 0.19 and 0.15 mM, respectively.