Coral-derived microorganisms have been historically proven to be prolific sources of bioactive secondary metabolites. Twelve benzopyranone and/or xanthone derivatives, including a new benzopyranone with an uncommon carboxyl group at C-8, coniochaetone K (1), were obtained from the Beibu Gulf-derived coral symbiotic fungusCladosporium halotoleransGXIMD 02502. Their structures were determined by extensive spectroscopic data interpretation and comparison with literature values. The absolute configuration of1was accomplished by comparison of specific optical rotation as well as quantum chemical ECD calculations. Thein vitrocytotoxicity of compounds1-12against two human prostatic cancer cell lines, C4-2B and 22RV1, were evaluated. And compounds1,3,6-8, and10-11demonstrated significant cytotoxicity with inhibitions ranging from 55.8% to 82.1% at the concentration of 10 mu M.