!A phytochemical investigation on the essential oil of Thuja orientalis resulted in the isolation and identification of three new sesquiterpenes, 3α-methoxy-4α-epoxythujopsane (1), Δ 3,15 -4β-epoxythujopsene (2), and Δ 3,4 -thujopsen-2,15-diol (3), together with eight known sesquiterpenoids (4-11). The structures of these new compounds were elucidated based on spectroscopic data analyses including extensive 2D-NMR data and HR-ESIMS. The full assignments of 1 H and 13 C NMR chemical shifts for thujopsadiene (4) were obtained by 2D-NMR for the first time. All compounds (1-11) showed antiproliferative activities against the SK-OV-3 and SK-MEL-2 cell lines with IC 50 values of 5. compounds 1,3,4,7,8, and 9 significantly inhibited nitric oxide production in lipopolysaccharide-activated BV-2 cells with IC 50 values of 3.93-17.85 µM without cell toxicity.