Objective: 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 Iba-1, MBP, NeuN and CD31, but which was not co-localized with 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.