Objective：This study aims to explore the expression of B cell-specific MLV integration site-1（Bmi-1）in mice spinal cord after spinal cord injury（SCI）. Methods：Two month-old C57Bl/6 mice received moderate contusion SCI at T9 using LISA impactor. The expression and cellular localization of Bmi-1 in spinal cord at the day of 1，3，7，14 and 28 post SCI were detected by Western blot and immunofluorescence staining. Results：The results of Western blot showed that the expression of Bmi-1 was increased and achieved a peak value at day one post SCI，and which was higher than normal till to the day 28 post SCI. The tendency of the Bmi-1 expression was consistent with the expression of proliferating cell nuclear antigen（PCNA）. The results of the immunofluorescence staining showed that the Bmi-1 was increased and co-localized with ionized calcium binding adapter molecule 1（Iba-1），myelin basic protein（MBP），neuronal nuclei antigen（NeuN），and platelet and endothelial cell adhesion molecule-1（PECAM-1/yCD31），but which was not co-localized with glial fibrillary acidic protein（GFAP）after SCI. Conclusion：The expression of Bmi-1 was increased and mainly localized in microglia，myelin cells，neuron and endothelium，and especially in microglia after SCI. It suggests that the expression of Bmi-1 may relate with the proliferation and activation of microglia，the endogenous remyelination，and the activity of the endothelium. The Bmi-1 may involve in the pathological process after SCI.