The ataxia telangiectasia mutated gene (atm) is a tumor-suppressing gene, locates in the human chromosome 11q22-23. This gene mainly participates in recognition and repairment of DNA damage and plays a critical role in signal transduction pathway induced by double strand breaks (DSB). In chronic lymphocytic leukemia (CLL) there is high frequency of loss of heterozygosity (LOH) and mutation of atm gene, which related to pathopoiesis and progression of CLL. This article reviewed the progress of recent studies on the characteristics and mechanism of atm gene, as well as its role in the pathogenesis of CLL.