Abstract: In order to analyze comparatively the similarities and differences of the volatile oils components from leaves of Syzygium samarangense Merr. et Perry and Melaleuca leucadendron L. and study their effects on the proliferation activity of A549 and H460 cells,the volatile oils from leaves of Syzygium samarangense Merr. et Perry and Melaleuca leucadendron L. were extracted by steam distillation. Their chemical constituents were analyzed by gas chromatography-mass spectrometry(GC-MS). Their effects on the proliferation activity of lung cancer A549 and H460 cells were evaluated by MTT assay. Results of GC-MS analysis showed that from the volatile oil of leaves of Syzygium samarangense Merr. et Perry,38 compounds were isolated and identified. The main constituents were caryophyllene,à-selinene,β-eudesmene,(+)-δ-cadinene and globulol.. From the volatile oil of leaves of Melaleuca leucadendron L.,28 compounds were isolated and identified. The main components were eucalyptol,(ñ)-2,6,6-trimethylbicyclo3.1.1hept-2-ene,α-terpineol,D-limonene and epiglobulol.These two volatile oils had 13 common compounds and their retention times were basically the same. The difference of was from 0.3 to 27 times. The structures and relative content of their five main components were not the same. The results of MTT assay showed that the volatile oil of leaves of Syzygium samarangense Merr. et Perry significantly inhibited the proliferation activity of human lung cancer cells A549 after 24 hours treatment at 40 mg/L(p<0.05)and significantly inhibited the proliferation activity of human lung cancer cells H460 at 60 mg/L(p<0.001)in a dose-dependent enhancement with IC₅₀ values of 49.99 and 65.70 mg/L. The volatile oil of leaves of Melaleuca leucadendron L. showed no significant growth inhibition against A549 and H460 cells(p>0.05). In conclusion,the Syzygium samarangense Merr. et Perry and Melaleuca leucadendron L.all belonged to Myrtaceae,but the amount of the compounds contained in the volatile oils of their dried leaves and the relative content of the same compound of them were different. The effects of the two volatile oils on the cell proliferation of human lung cancer cells A549 and H460 were also different.