Two pairs of salicylaldehyde derivative enantiomers, euroticins A and B (1 and 2), were isolated from a marine-derived fungus Eurotium sp. SCSIO F452. Compound 1 possesses a highly constructed 6/6/6/5/7 pentacyclic structure featuring an unprecedented 2,11-dioxatricyclo[5.3.1.04,8]undecane core. Compound 2 represents the first example of 6/6/6/6 tetracyclic salicylaldehyde derivative. Their structures were established by spectroscopic analyses, X-ray diffraction, and electronic circular dichroism (ECD) and 13C NMR calculations. Compounds (+)-2 and (-)-2 exhibited remarkable antioxidative activities.