Abstract: As a member of the immediate early gene family, immediate early response gene X-1(IEX-1) participates in multiple biological effects of the cells.Several factors, such as NF-κB, 1a-25(OH) 2D3, UVB, AP2, SPl, P53, and TNF-a can modulate IEX-1 expression and transcription.Studies have shown that IEX-1 expression and transcription are down-regulated or absent in many tumor cells.The IEX-1 gene can be activated at an early stage in many types of tumor and normal cells by ionizing radiation.IEX-1 activation and consequent expression are closely related to the change of irradiated cell growth, cell cycle, and apoptosis.The radiation-induced characteristics of IEX-1 gene bestows it potential for clinical and genetic engineering production.