Down-regulated in renal cell carcinoma gene (DRR1) is one of the candidate tumor suppressor genes (TSGs) on human 3p21.1. This study was performed to validate the expression status of DRR1 gene in cancer cells and the expression pattern of the protein in clinical specimens of human lung cancer and to examine its potential as a molecular target for treatment of lung cancer in vivo. DRR1 expression was analyzed in 7 human lung cancer cell lines. DRR1 protein expression was also examined in clinical non-small cell lung cancer (NSCLC) specimens. Furthermore, effects of DRR1 re-expression on A549 cells in vitro and A549 xenograft tumors in nude mice were evaluated. Loss of DRR1 mRNA expression was detected in 6 of the 7 human cancer cell lines, the exception was the renal cancer cell line OS-RC-2. DRR1 protein expression was absent in 15 of 20 (75%) human NSCLC specimens by immunostaining. Transfection of DRR1 gene into DRR1-negative-expressing A549 cells resulted in significant cell growth suppression and apoptosis. Plasmids containing DRR1 cDNA complexed with DOTAP:Chol liposomes were administered intravenously via tail vein to nude mice bearing A549 xenograft tumors resulting in tumor growth inhibition and elevation of apoptosis compared with the controls. DRR1 is a potent growth suppressor of NSCLC, acting through apoptosis pathway in vivo and it may be a potential therapeutic gene for human lung cancer.