Thymosin beta15 (Tbeta15) is a small protein that comprises 44 amino acid residues. Tbeta15 is upregulated in malignant human prostate and breast tumors. The expression of Tbeta15 correlates with the metastatic potential of mouse lung cancer and human breast carcinoma cells. However, the correlation of Tbeta15 expression with human lung cancer remains unclear. Using immunohistochemistry and in situ hybridization, we analyzed the expression of Tbeta15 in tumors and tumor-adjacent tissues obtained from 76 patients with non-small cell lung cancer (NSCLC). The relationship between Tbeta15 expression and clinicopathological factors was investigated. Our findings showed that in NSCLC, Tbeta15 protein and mRNA were mainly expressed in the cytoplasm, and their expression correlated with stage (p=0.018 for both), differentiation (p=0.013 and 0.006, respectively), and lymph node metastasis (p=0.001 and 0.009, respectively). Tbeta15 expression was examined in PG-BE1 and PG-LH7 lung cancer cells. We found that both Tbeta15 protein and mRNA were highly expressed in BE1 cells as compared to LH7 cells. After transfecting the PG-LH7 cells with the pEGFP-Tbeta15 plasmid in order to increase Tbeta15 expression, the migration ability of the cells was enhanced. These findings suggest that increased Tbeta15 expression correlates with the progression and metastasis of NSCLC.