The chemical composition of the essential oil of Chamaecyparis formosensis wood has been examined. GC-MS data and retention indices for reference samples were used to identify 32 constituents. α-Eudesmol (18.06%), β-guaiene (8.0%), (–)-β-cadinene (7.89%), γ-costal (7.03%), α-muurolol (6.49%), 4α-hydroxy-4β-methyldihydrocostol (5.52%), σ-selinene (4.78%), santolina triene (4.60%), eremophilene (4.32%), humulene (4.11%), myrtenol (4.11%), and τ-cadinene (3.25%) were the most abundant components. Tests with the typical wood decay fungi, Laetiporus sulphureus and Trametes versicolor , proved the antifungal activity of the oil, as the growth of L. sulphureus and T. versicolor was inhibited at concentrations of 50 and 100 μg ml −1 , respectively. The following characteristic volatile compounds were isolated and purified from ethyl acetate fractions: epi -cubenol, chamaecynone, myrtenol, cis -myrtanol, 12-hydroxyisointermedenol and 4α-hydroxy-4β-methyldi-hydrocostol. Chamaecynone possessed the strongest antifungal activity, with an antifungal index of 88.2% and 67.3% for L. sulphureus and T. versicolor at a dose of 50 μg ml −1 , respectively.