Background: Endogenous neural progenitor cells (NPC) found in the ependymal layer and the sub-ependymal area of the spinal cord are reported to respond to traumatic spinal cord injury (SCI). These cells have the potential to be manipulated as a novel approach for the repair of injured spinal cord. However, there is little known about the time course of NPC responses, nor the interactions with inflammatory cells and glial scar. Hypotheses: There is a critical time period for endogenous NPC response following SCI, and this relates to the reaction of glial scar and inflammatory cells. Methods: A mild contusion SCI model in rats was used to assess the response of endogenous NPC (anti-Nestin immunohistochemistry) at 24 hours, 1 week, 2 weeks and 6 weeks post-injury along with normal controls (0 hour  & 6 weeks) and sham controls (6 weeks). The endogenous NPC response was correlated to the inflammatory stage by examining neutrophils (H&E), microglia/monocytes (anti-ED1) and glial scar (anti-GFAP). Results: The response of endogenous NPC peaked at 24 hours (ANOVA, p<0.001) and then gradually declined. There were negative correlations of the endogenous NPC response with the formation of glial scar at lesion edge and the responses of microglia/monocytes at lesion site respectively (r>0.78, p<0.001), while the endogenous NPC were positively correlated with neutrophils (ρ=0.56, p<0.001). Conclusion: It was shown that the endogenous NPC had followed a definite temporal pattern in response to traumatic SCI and that the NPC response was negatively influenced by the formation of glial scar at lesion edge as well as the response of microglia and monocytes at lesion site. The early upregulation of neutrophils and NPC was likely to be driven by the pro-inflammatory cytokines released from neuron and activated microglia within hours.