The chemical compositions of the volatile oil from the leaves of Uncaria sessilifructus Roxb., obtained by hydrodistillation, was analyzed by gas chromatography-mass spectrometry. A total of 70 compounds were identified representing 97.62% of total oil composition. Major components of the volatile oil were esters (30.45%)> alkane (12.45%)> olefine aldehyde (11.69%)> alkene (11.02%)> Ketene (8.06%), the large concentrations of the chemical composition is methyl salicylate, fumaricacid, tetradecyl trans-hex-3-enyl ester, squalene, bicyclo[2.2.1]heptane analysis based on principal components of Uncaria sessilifructus Roxb. The results showed that established GC-MS analysis method can comprehensively reflect the compositions of the volatile oil from the leaves of Uncaria sessilifructus Roxb. , and provide scientific evidences for further exploitation.