Abstract: To analyze the chemical composition of the essential oil of Macleaya cordata, the essential oil was extracted from M. cordata by steam distillation, and then an analysis was conducted by applying GC-MS. The result shows that 48 ingredients have been found, and 39 of them have been identified, accounting for 92.464% of the total essential oil. The main chemical components of M. cordata are: 2-Methoxy-4-vinylphenol（11.270%）, Benzoic acid, 4-nitroso-, ethyl ester（11.178%）, 2-Hexenal, (E)-（10.415%）, Cedrol（7.371%）, 2-Undecanone, 6,10-dimethyl-（6.929%）, Phthalic acid, isobutyl octyl ester （5.700%）, 2-Phenylpropenal（4.509%）etc.