AbstractAntiradical and antioxidant activities of ethanolic extract and its fractions from Calocedrus formosana Florin heartwood were investigated, and active compounds were identified by spectral analyses. Among extract and three fractions, the ethyl acetate soluble fraction had a high total phenolic content and exhibited the desirable reducing power, antiradical activity, and antioxidant activity. The compounds haplomyrfolin, O-ethyl-α-conidendral, matairesinol, 7,8-dehydro-4-O-methyl-thujaplicatin, and 5-methoxy-isosalicifoline were isolated from antioxidative activity guided fractionation of the ethyl acetate soluble fraction. Haplomyrfolin and O-ethyl-α-conidendral were for the first time isolated and identified from C. formosana. Matairesinol and 5-methoxy-isosalicifoline exhibited superior DPPH radical scavenging ability and antioxidant activity, as evaluated by TEAC assay. Results obtained in the present study revealed that ethyl acetate soluble fraction from C. formosana heartwood extract and its active compounds, matairesinol and 5-methoxy-isosalicifoline, exhibit antioxidant potential as natural nutraceuticals.