Background: Aromatase alongside with estrogen receptor beta (ERβ) is a potential target for novel therapeutic strategy in lung adenocarcinoma (AC). The purpose of this study is to examine the correlations of expressions of aromatase and ERβ with other prognostic factors including epidermal growth factor receptor (EGFR) in lung AC. Methods: We analyzed 186 consecutive patients with lung AC who underwent surgical resection at Gunma University Hospital between Dec. 2003 and Feb. 2010. The clinicopathological characteristics and survivals of patients were subclassified based on the expressions of aromatase, ERα, ERβ, and progesterone receptor (PR) as determined by immunohistochemical staining. Gene alterations of EGFR and KRAS were evaluated with SmartAmp2. Multivariate analysis using Cox regression model was carried out to evaluate the effect of aromatase expression. In vitro experiment was performed with shRNA transduced aromatase-depleted lung AC cells. Results: Expressions of aromatase, ERα, ERβ, and PR were detected in 86.6%, 1.6%, 78.5%, 2.7% of all patients, respectively. In all patients, the expression of aromatase is an independent prognostic factor in OS (Hazard Ratio [HR] = 2.1; 95% confidential interval [CI], 1.2-3.6; P= .008) and RFS (HR = 1.8; 95%CI, 1.1-2.8; P= .022), while that of ERβ is not statistically significant. In patients with wild-type EGFR, high aromatase expression is also an independent prognostic factor in OS (HR = 2.4; 95%CI, 1.2-4.6; P= .009) and RFS (HR = 2.5; 95%CI, 1.3-4.7; P= .006). Interestingly, high aromatase expression is significantly correlated with poor survival only in women (OS, P= .019; RFS, P= 0.033) in patients with wild-type EGFR, while no prognostic significance is observed in patients with EGFR mutations. In line with this, depletion by shRNA of aromatase suppressed oncogenic activity in soft agar assays. Conclusions: Aromatase expression is independent negative prognostic factor in especially EGFR wild-type adenocarcinoma. We further showed that in patients with wild-type EGFR, high aromatase expression is a significant correlated with poor survival only in women. Aromatase-depleted lung AC cells transduced shRNA, demonstrate decreased tumorigenicity.