The aims of this study were to investigate the efficacy of acupuncture on myoelectrical activity of inflamed or normal colon in the rat, and whether the effect of acupuncture on colonic motility was related to endogenous opioids. Twenty-two male Sprague-Dawley rats were divided into three groups. Experimental groups were normal group (n = 8), colitis group (n = 6) and naloxone group (n = 8). Stainless steel bipolar electrodes were implanted on the serosal layer of the proximal colon of rats. Colitis was induced 7 days after electrode implantation using trinitrobenzene sulphonic acid (TNBS) and ethanol. Electromyograms (EMG) were recorded by using polygraph 11 days after implantation of electrodes. In normal group, normal colonic motility was recorded for 60 min, and then traditional acupuncture at GV-1 was applied for 20 min and EMG was recorded for further 60 min in untreated rats. In colitis group, after recording of basal colonic motility for 60 min, 20 min of acupuncture treatment and further EMG recording was performed for 60 min in TNBS/ethanol treated rats. In naloxone group, following subcutaneous administration of naloxone (3 mg/kg), recording of EMG and acupuncture treatment were performed in TNBS/ethanol treated rats. In the normal group, acupuncture at GV-1 did not induce significant changes in colonic motility. TNBS/ethanol treatment had no significant effect on the frequency of colonic motility. And in colitis group, GV-1 acupuncture significantly decreased colonic motility (p < 0.01). In naloxone group, after injection of naloxone, acupuncture at GV-1 did not change colonic motility in TNBS/ethanol treated rats. On the inflamed colon, naloxone blocked the effect of acupuncture. The present results suggested that endogenous opioids released by acupuncture at GV-1 decrease the motility of inflamed colon in rats, but not normal colon.