Abstract: Objective To determine the expression of carcino embryonie antigen（CEA）in serum and pleural effusion in patients with lung adenocarcinoma and its relationship with epidermal growth factor receptor（EGFR）mutations. MethodsSeventynine serum and pleural effusion samples were collected from 79 lung adenocarcinoma patients with malignant pleural effusion. The concentration of CEA was detected by immunoradiometric assay， and the relationship between the level of CEA and EGFR mutations was analyzed. ResultsA total of 35 cases involved EGFR mutations， and the mutation rate of EGFR was 44.3％（35/79）. For the serum CEA， the area under curve（AUC） was 0.661（95％CI：0.536-0.785）. When the cut-off value was 19.5 ng／ml， the efficacy of sensitivity and specificity were best. For the pleural effusion CEA， when the cut-off value was 55.5 ng／ml， the AUC was 0.757（95％CI：0.653-0.862）. The mutation rate was significantly higher in the patients with high serum（≥19.5 ng／ml）and pleural effusion（≥55.5 ng／ml）levels of CEA than those with low expression levels（P＜0.05）. Moreover， the positive rates of EGFR mutations of the three groups（both≥cut-off， any of them≥cut-off and both ＜cut-off）were 64.3％， 60.0％，16.1％， respectively（P＜0.001）. In a multivariate regression analysis， the level of pleural effusion CEA（HR： 1.002， 95％ CI：1.001-1.004， P=0.003）was confirmed as independent factor of predicting EGFR mutations. Conclusion CEA can probably serve as a marker of predicting EGFR mutations.