In the present study, we demonstrated i) TTF-1 mRNA expression in human lung cancer cell lines had very low frequency, ii) overexpressed TTF-1 increased apoptosis and repressed the expression of Ki-67 in A549 cell line and iii) strong immunohistochemical expression of TTF-1 was statistically associated with well-differentiated phenotype and inverse correlation with Ki-67 expression in Xuanwei lung adenocarcinomas. The gene discussed is MKI67; the disease is lung adenocarcinoma.