Adenosquamous carcinoma of the lung (Ad-Sq) is an uncommon subtype with poor prognosis. We analyzed the clinicopathological characteristics of Ad-Sq, focusing the correlation between Epidermal Growth Factor Receptor (EGFR) mutation and clinicopathological factors. A total of 67 cases were selected from September 1992 to May 2011. EGFR mutational analysis (n = 59) was performed by direct sequence. We also performed immunohistochemical staining for EGFR mutated cases using the two mutation-specific antibodies for deletion and L858R. Postoperative 3-year survival rate of Ad-Sq was 58.7%, statistically worse in comparison with adenocarcinoma (58.7% vs. 78.1%, P = 0.038). Twenty-four percent (14/59) were positive for EGFR mutations. Patients who had never been smokers and who were lymphatic permeation positive were seen more frequently in the mutation positive group (P = 0.035, 0.027, respectively). Moreover, the EGFR mutated group tended to have a more positive prognosis than negative. Focusing on the pathological features, the lepidic growth pattern was more frequently seen in the positive group (P = 0.018). Immunoreactivity for the DEL-specific and L858-specific antibody were observed in both adenocarcinoma and squamous cell carcinoma components. Our study demonstrated that EGFR mutated Ad-Sq had similar clinicopathological features as EGFR mutated adenocarcinoma.