DLC1 (deleted in liver cancer-1) is a new candidate tumor suppressor gene, which is inactive in various types of human cancers including colon cancer. To study the function of DLC1, we constructed a pcDNA3.1 vector containing the DLC1 gene and transfected it into HT29 colon cancer cells that were deficient in DLC1 expression. The restoration of DLC1 expression in HT29 cells significantly inhibited cell proliferation and migration. Flow cytometry showed that DLC1 transfection into HT29 cells induced apoptosis and that the cell cycle was arrested at S-phase. Additionally, cyclinD1 mRNA and protein expression were down-regulated while p21 expression was increased in pcDNA3.1-DLC1-HT29 cells compared to wild HT29 cells. These results confirm the role of DLC1 gene as a tumor suppressor, which may be manifested by regulation of p21 and cyclinDl. The DLC1 gene has a potential therapeutic role in inhibiting the development of colon cancer.