Abstract: A new polyketide:3R, 5R-(-)-talaroflavone (2), along with 15 known compounds were isolated from a EtOAc extract of a sponge-derived fungus Alternaria sp. F49. Compounds 1-2 and 3-4 were separated as two pairs of enantiomers by chiral HPLC from Ⅰ and Ⅱ. The structures of compounds 1-16 were elucidated by means of NMR and MS. Furthermore, the absolute configurations of compounds 1-2 were determined by single crystal X-ray diffraction experiment and CD analyses. Compounds 6, 8-10 were isolated from this genus (Alternaria sp.) for the first time. Compound 16 showed moderate COX-2 enzyme inhibitory activity with IC₅₀of 7.3 μmol·L^-1.