Overexpressed Angiopoietin-2 (Ang-2) derived mainly from cancer cells was reported to promote tumor angiogenesis. The aim of this study was to evaluate the expression of Ang-2 in non-small cell lung cancers (NSCLCs). We investigated Ang-2 expression in 77 patients with NSCLC who underwent curative tumor resection by means of reverse transcription-polymerase chain reaction (RT-PCR). We also determined whether or not expression of Ang-2 mRNA correlates with immunohistochemical assays of Ang-2 protein and microvessel density (MVD) level. The level of Ang-2 mRNA expression was presented by the relative yield of each gene to the S14 mRNA, respectively. Ang-2 mRNA expression in NSCLC was significantly greater than that in non-cancerous normal lung (p=0.0178). The Ang-2 mRNA expression was significantly associated with lymph node metastasis, stage, Ang-2 protein, and microvessel density (MVD) level (p=0.0009 for lymph node metastasis; p=0.0002 for stage; p<0.0001 for Ang-2 protein; p<0.0001 for MVD). With regard to prognosis, the overall and stage I survival rates for patients in the high Ang-2 mRNA expression group were significantly poorer when compared with the low Ang-2 mRNA expression group (p<0.0001 for overall; p=0.0201 for stage I). Furthermore, expression of Ang-2 mRNA was an independent predictor of prognosis by multivariate analysis (p=0.0028). These data indicate that Ang-2 may contribute to tumor angiogenesis and progression and that Ang-2 gene expression can serve as a useful prognostic marker in NSCLC.