Objective: To compare normal rat and rat with chronic spinal cord injury (SCI) with CMG and EUS after intravesical capsaicin or given s.c to determine the role of capsaicin-sensitive bladder afferents in micturition. Methods: Male Sprague-Dawley rats, normal or with spinal cord transection at the level of T 9-10 . CMG and EUS-EMG tests were carried out before and after administration of capsaicin intravesically or s.c 8 weeks after SCI. Results: Capsaicin given subcutaneously induced the nonvoiding bladder contractions in normal rats. After administration rats had large voiding volume(VV) and residual volme (RV) ,voiding efficiency(VE) was decreased ,but micturing press(MP) was not affected. Intravesical capsaicin also decreased VE with the MP non affected. In SCI rats the nonvoiding bladder contractions induced by infusion of saline before voiding can be eliminated by capsaicin (125 mg/kg s.c) .But intravesical capsaicin can inhibit the reflex bladder contraction in SCI rats. Conclusion: The data indicated the capsaicin sensitive bladder afferents take part in the initiation of reflex micturition in both normal and SCI rats .In normal rats activity in the capsaicin sensitive fibers initiated by bladder filling keep the compliance of bladder .In SCI rats these afferents do contribute to hyperactivity of the bladder during the filling phase of the CMG.