Cells and organisms respond to various stresses when exposed to the heat and pressure, and physical stimulation. Response to the stress can be regarded as a role of a defense strategy for maintaining homeostasis. In plants, tolerance to low temperature was carried out by the removal of ROS (Reactive Oxygen Species), accumulation of sugar, and controlling hormones. On the other hand, there is little report about the cold stress response in mammals, because they are homeothermic animals. In this study, we elucidated a possible mechanism for response to cold stress in HaCaT cell as a human epidermal cell model. First, we evaluated the viability of HaCaT cells by staining calcein-AM and propidium iodide after 4℃ cultivation. Increase of dead cells was observed from 12 h after cultivation at 4℃. In addition, increase of intracellular Ca^<2+> concentration and mitochondrial ROS was observed from 12 h after cultivation at 4℃. Proportion of cell death was reduced when mitochondrial ROS generation was inhibited using antioxidants NAC (N-acetyl-L-cysteine) but intracellular Ca^<2+> concentration was not changed at all. Overall, induction by cold stress-mediated, cell death may be related to by mitochondrial ROS in HaCaT cell.