Objective:To investigate the expression of axon guidance cue slit-2 mRNA, and the ethology and morphology changes in different phases of spinal cord injury(SCI) development. Methods:Forty Sprague-Dawley rats were randomly divided into normal group, sham operation group and operation group which include 6 subgroups(1,3,7,14,21,28 days). The spinal cord hemisection injury model was made by cutting the posterior right side spinal cord. Function changes in the right posterior limb were evaluated by BBB method, the general morphology changes were observed by HE stain, and the expression of slit-2 mRNA was detected through in situ hybridization methods. The positive cells were analyzed by a computer image analysis system. Results:The limb function of experimental rats significantly recovered from 7 d to 28 d. The morphology gradually changed from local hematoma to inflammatory cell infiltrate, scar formation and vacuolar degeneration of the distal as well as the proximal spinal cord tissue. The in situ hybridization results indicated that expression of slit-2 mRNA in the angulus anterior was low in either normal or sham operation group, but significantly increased at 3 d(P < 0.01) in the operation group, then it decreased significantly at 7 d and 14 d(P < 0.05), and continued expression until 28 d. Meanwhile, in 7 d group, the expression of slit-2 mRNA was obviously rising up in the reactive hyperplasia cells around the lesion incision. Conclusion:The injury of adult mammalian spinal cord is a dynamic complex course. The axon guidance cue slit may act as a inhibitory role to repel axon regeneration via mediating migration of inflammatory cells, interacting with several neurogen or cues, participating formation of the scar and other probable mechanisms.