Abstract: Objective: To investigate the antinociceptive effect of BTX-A and its influence on the serumal TNF in an acetic acid-induced visceral pain model in rats.Methods: Male Wistar rats of postnatal eight weeks were divided into four groups: BTX-A（2U,4U,and 6U） or vehicle（2 mL） was injected intraperitoneally of B,C,D and A group rats.Four weeks later,6 rats of every group were performed with colorectal balloon distention to evaluate colorectal pain threshold.Rats were challenged with acetic acid（2%,3 mL/kg）intraperitoneal injection 1 week and 4 weeks.Abdominal writhing behaviors were monitored in 45 minutes as indicators of pain.The serumal TNF was tested by radioimmunology.Results: The colorectal pain thresholds in group B,C,D were not significantly difference from those in the saline group at week 4.At the end of one week,total writhing test scores in 45 minutes of group C and D were decreased significantly compared with group A（P＜0.05）;Only the serumal TNF levels of group D were lower than group A;At week 4,the writhing sores of group B,C,D and serumal TNF levels of group C,D all showed significant decrease compared with those of group A（P＜0.05）.Conclusion: Injection of BTX-A intraperitoneally significantly reduces acetic acid-induced nociceptive behaviors after 1 week and 4 weeks,decreases the level of serumal TNF.Such an antinociceptive effect of BTX-A is postulated with the inhibition of acid-induced release of inflammatory factor TNF in serum.