Abstract: The antitumor activities of volatile constituents from Platycladus orentalis against human lung cancer cell line NCI-H460 were determined by alamar blue assay.The results showed that the inhibiting rates of volatile constituents from the leaves,seed and seed capsule of P.orentalis against human lung cancer cell line NCI-H460 were 86.24%,97.73% and 47.80% respectively.And the volatile oil constituents in leaves and seed were the highest.The volatile constituents from the three organs were analyzed by GC-MS method.The varieties of volatile oil in the leaf,seed and seed capsule of P.orentalis were 8,31 and 21 respectively.The results showed that the leaves contained the highest contents of α,α,4,8-tetramethy 1-3,7-cyclodecadiene-1-methjanol and cedrol,which took about 27.213% and 26.193% respectively.The contents of cedrol in seed and seed capsule were the highest,which were 28.277% and 26.919% of the total.The purity of cedrol re-crystallized under 4 ℃ from leaves of P.orentalis was as high as 97.06%.The IC50 of cedrol against the lung cancer cell line NCI-H460 was 44.98 μg·mL-1.