【Objective】To investigate the mechanisms implicated in ataxia telangiectasia mutated（ATM）inhibition-caused apoptosis in the cultured cerebellar granule neurons.【Methods】Primary cerebellar granule neurons（CGN）isolated from neonatal Sprague Dawley rats of 7-8 days were divided into the following groups：25 K group（survival group），5 K group（apoptosis group）and 25 K + KU-55933 treatment group（ATM inhibition group），25 K + KU-55933 + Mithramycin A treatment group（MMA group），25 K + KU-55933 + Chromonycin A3 treatment group（CMA3 group）. The protein expression of p-ATM，ATM，Bim and Caspase 3 were detected by Western Blot. The apoptotic cells with nuclear pyknosis were detected by Hoechst-staining. 【Results】Compared with 25 K group ，the result of western blot showed that the protein expression of Bim and Caspase 3 were increased in the ATM inhibition group（P < 0.05）. Compared with 25 K group， the nuclear pyknosis rate of 5 K group and ATM inhibition group were significantly increased（P < 0.05）. Inhibition of Bim by Mithramycin A or Chromomycin A3 remarkably reversed ATM inhibition-caused apoptosis. 【Conclusion】Inhibition of ATM induce Bim dependent apoptosis in cultured cerebellar granule neurons.