The upregulated expression of JMJD6 was observed in various human cancers. However, little was known about JMJD6 expression and its clinicopathological significance in lung adenocarcinoma. The aim of this study was to investigate the expression and significance of JMJD6 in lung adenocarcinoma progression and prognosis. The levels of JMJD6 mRNA and protein in lung adenocarcinoma specimens and corresponding non-tumorous lung tissues were evaluated by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) and Western blot. In order to investigate the correlations between JMJD6 and the clinicopathological features of lung adenocarcinoma, the expression of JMJD6 in 154 patients with lung adenocarcinoma was detected by immunohistochemistry. By qRT-PCR and Western blot, the relative expression levels of JMJD6 mRNA and protein were significantly higher in lung adenocarcinoma tissues than in corresponding non-tumorous lung tissues (P < 0.001). Immunohistochemical staining revealed that high JMJD6 expression was closely correlated with tumor size (P = 0.005), pathological grade (P = 0.003), pT status (P = 0.012), pN status (P = 0.003), and pleural invasion (P < 0.001). Moreover, the results of Kaplan-Meier analysis indicated that a high expression level of JMJD6 resulted in a significantly poor prognosis of lung adenocarcinoma patients. Multivariate analysis showed that the status of JMJD6 expression was an independent prognostic factor for lung adenocarcinoma patients. Our results showed that JMJD6 plays a key role in lung adenocarcinoma and therefore may provide an opportunity for developing a novel therapeutic target as well as a prognostic marker in lung adenocarcinoma.