Radiation has been an effective tool for treating cancer for a long time. Radiation therapy induces DNA damage within cancer cells and destroys their ability to reproduce. Radiation therapy is often combined with other treatments, like surgery and chemotherapy. Here, we describe the effects of radiation and histone deacetylase inhibitor, Trichostain A, on cell cycle regulation in hepatoma cells. The combinatorial treatment of radiation and Trichostain A induced cell cycle arrest and thereby increasing the hepatoma cell death. Furthermore, the regulatory effects of radiation and Trichostatin A on cell cycle applied in cell type specifically. These results suggest that the treatment of radiation and Trichostatin A may play a central role in hepatoma cell death and might be a good remedy to improve the efficiency of radiation therapy.