Objective To observe the changes of myelin sheath in corpus callosum on non-ischemic side after ischemic stroke in rats with cerebral ischemia/reperfusion (I/R) model, and to investigate the effect of vagus nerve stimulation (VNS) on secondary demyelination in I/R model. Methods Forty-two rats were randomly assigned to sham, I/R, or I/R＋VNS groups, with 14 rats in each group. Except for the sham group, the rats in other groups were used to construct I/R model by a middle cerebral artery occlusion thread method. In addition, the rats in the I/R＋VNS group were given repetitive electrical stimulation of the left vagus nerve for 60 min at 30 min after ischemia occlusion. The cerebral infarction volume was observed by 2,3,5-triphenyltetrazolium chloride staining. The expression levels of myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) in the corpus callosum on the non-ischemic side were detected by Western blotting. The integrity and thickness of myelin sheaths in the corpus callosum on the non-ischemic side were observed by Luxol fast blue staining and transmission electron microscopy, respectively. Results Compared with the sham group, the volume of cerebral infarction in the I/R group was increased (P＜0.01). On the 3^rd day after I/R, compared with the sham group, the expression levels of MBP and MAG were significantly decreased (both P＜0.01), the intensity of Luxol fast blue staining was significantly decreased (P＜0.01), and the thickness of the myelin sheath was significantly thinner (g-ratio was increased, P＜0.01) in the corpus callosum on the non-ischemic side. Compared with the I/R group, the expression levels of MBP and MAG in the I/R＋VNS group were significantly increased (both P＜0.05), the intensity of Luxol fast blue staining was significantly increased (P＜0.01), and the thickness of myelin sheath was significantly increased (g-ratio was decreased, P＜0.01) in the corpus callosum on the non-ischemic side. Conclusion Secondary demyelination occurs on the non-ischemic side of the rat corpus callosum after ischemic stroke, and VNS can ameliorate the demyelination.