Three novel 2,3-diaryl indone derivatives, ascomindones A-C (1-3), and two new isobenzofuran derivatives, ascomfurans A (4) and B (5), together with four know compounds (6-9) were isolated from the culture of a mangrove-derived fungus Ascomycota sp. SK2YWS-L. Their structures were elucidated on the interpretation of spectroscopic data. 1 and 4 were further constructed by analysis of X-ray diffraction. Antioxidant properties based on 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical scavenging activities and the ferric reducing ability power (FRAP) of the new compounds were assayed. All of them exhibited significant effects, of which 1 showed more potent activity than ascorbic acid in scavenging DPPH radical with IC50 value of 18.1 μM.