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 gamma (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 gamma 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 y caused cell cycle arrest at G2/M transition when transfected into Hep-G2 cells. Therefore, the possible role of GADD45 gamma in cell growth control was further confirmed in this paper.