Calocedrus formosanaFlorin (Cupressaceae) is an endemic tree species in Taiwan; its timber is recognized for natural decay resistance. To examine the antitermitic and antifungal activities of leaf essential oil and its main constituents, C. formosanaleaves were extracted and the essential oils analyzed by GC-MS. Bioactivity tests against the termite Coptotermes formosanusdemonstrate that the LC50value of leaf essential oil is 27.6 mg/g. Furthermore, exposure to T-muurolol caused 100% mortality at a dosage of 5 mg/g after 14 d. Leaf oil constituents displayed activity against four fungi, Lenzites betulina, Pycnoporus coccineus, Trametes versicolor, and Laetiporus sulphureus. Two compounds, α-cadinol and T-muurolol, exhibited the strongest antifungal activity. The LC50values of α-cadinol against L. sulphureus, L. betulina, and T. versicolorare 9.9, 28.6, and 30.4 μ g/ml, respectively.