To investigate the significance of FOXO3a and Ki67 in human lung adenocarcinomas. Envisionimmunohistochemical staining and Western blotting were used to examine the protein expression of FOXO3ain 127 cases of human lung adenocarcinoma specimens. The positive rate in lung adenocarcinoma (55.9%) waslower than that in normal tissues (80%). We found that the expression of FOXO3a was closely related with thedegree of differentiation, TNM staging, lymph node metastasis and survival. In addition, significant differencesin the different pathological types of lung adenocarcinoma cases (P<0.01). The FOXO3a positive rate of the acinias the main type (APA) (86.7%) and the lepidic as the main type (LPA) (82.4%) was higher than the solid asthe main type (SPA) (50.0%), the papilla as the main type (PPA) (42.9%) and the micropapilla as the main type(MPA) (9.4%). Moreover, the expression of FOXO3a was negatively related with Ki67 expression. Our resultssuggested that the expression of FOXO3a is closely correlated with the aggressiveness of lung adenocarcinoma.It was indicated that disregulation of FOXO3a might play key roles in the occurrence and development of lunga denocarcinoma and joint detection of the two markers might play an important role in diagnosing tumors.