Objective · To investigate the changes of rectal smooth muscle structure after spinal cord injury in rats. Methods · Twenty adult female Sprague-Dawley rats were randomly divided into two groups, i.e., spinal cord injury group and control group. In the spinal cord injury group, the spinal cord was completely disconnected between L5 and L6, and control group was not surgically treated. After 3 months, gastric instillation was used to measure the intestinal transit time with the administration of activated carbon suspension and the mass of fecal pellets within 24 h was recorded. Then the rectal tissue was taken at about 1 cm proximal to the anus. The changes of rat rectal smooth muscle were detectedhematoxylin-eosin (H-E) staining, Masson staining and immunohistochemistry staining. Results · Gastric instillation showed that compared with control group, the intestinal transit time of spinal cord injury group significantly prolonged, and the mass of fecal pellets within 24 h significantly reduced. H-E staining showed that the arrangement of rat rectal smooth muscle cells was disordered after spinal cord injury. Masson staining showed fibrotic changes in the rectal smooth muscle layer of rats after spinal cord injury. Immunohistochemistry staining showed that the of α smooth muscle actin (α-SMA) in rat rectal smooth muscle decreased after spinal cord injury. Conclusion · After spinal cord injury, rats present defecation dysfunction. The structure of rectal smooth muscle also changes significantly, mainly including smooth muscle atrophy, fibrosis and decreased α-SMA .