Lung adenocarcinoma with a preoperatively elevated serum carcinoembryonic antigen (CEA) value has a relatively poor postoperative prognosis. Although surgical resection generally results in a reduction in the CEA value, the significance of the change in the CEA value on the prognostic outcome remains unclear. Our study included 133 patients who underwent lobectomy with curative intent for lung adenocarcinoma representing a preoperative CEA value > 5.0. Statistical analysis was performed using a receiver operating characteristic analysis and a stepwise Cox proportional hazards analysis. Both the postoperative CEA value and postoperative-to-preoperative CEA ratio (CEA ratio) significantly affected the survival. Although the CEA ratio was not predictive of the survival in patients with postoperative CEA ≤ 6.2ng/ml (n = 105), it was predictive in the remaining patients with postoperative CEA > 6.2ng/ml (n = 28). Patients with postoperative CEA > 6.2ng/ml and a CEA ratio ≥ 0.39 (n = 7) showed the worst survival outcome. According to the multivariate analysis, the CEA ratio and postoperative nodal status were significant predictors of the survival in overall patients. The CEA ratio may be a useful prognostic marker in patients who undergo lobectomy for lung adenocarcinoma and show postoperative CEA > 6.2ng/ml. A high CEA ratio may indicate the presence of a subclinical residual tumor, which may lead to the development of subsequent recurrence.