Aim of this study: Mitochondrial undergoes fragmentation in response to ischemia/reperfusion,and inhibiting mitochondrial fission protects against heart ischemia/reperfusion injury.Ginsenoside-Rb1,a main active constituent of ginseng,exerts cardioprotective effect against ischemia/reperfusion injury.However,its effect on mitochondrial fission in reperfused heart has not been investigated yet.In this study we investigate the effect of Ginsenoside-Rb1 on mitochondrial fission induced by hypoxia/reoxygenation (H/R) in neonatal rat cardiomyocytes Materials and methods: mitochondrial fission and apoptosis were induced by H/R.Expressions of Drp1,Fis1,Mfn1,Opa1 mRNAs were determined by real time PCR,Drp1 and p53 proteins levels were assessed by western bloting,mitochondrial morphology changes were analyzed by confocal microscope,ROS levels and cells apoptosis were detected by flow cytometry.