Growth-arrest and DNA-damage inducible (GADD) genes and Myeloid differentiation primary response (MyD) genes represent a family of genes that play a key role in negative control of cell growth. In the present study, following clone and location of human GADD45 γ (MyDL) gene, we have found that its mRNA expression level was down-regulated in 15/23 cases of clinic hepatocellular carcinoma (HCC) by comparing the northern hybridization results between the tumor tissues and adjacent normal tissues. Transient transfection of GADD45 γ cDNA with intact open reading frame sequence into the human hepatoma cells Hep-G2 resulted in dramatic growth suppression in colony formation assays. Furthermore, flow cytometry analysis indicated that GADD45 γ caused cell cycle arrest at G2/M transition when transfected into Hep-G2 cells. Therefore, the possible role of GADD45 γ in cell growth control was further confirmed in this paper.