Objective:To observe the effect and the mechanism of Immature Orange Fruit & Paeonia Powder(IOFPP) on the visceral hypersensitivity in rats.Methods:The visceral hypersensitivity rats induced by chronic stress excitation were used to observe the action of IOFPP on the intestinal tract sensitivity and mast cell(MC) count and substance P(SP) immunoreaction masculine fiber level in ileo-appendix and colon mucosa underlayer.Results:IOFPP can increase the visceral minimum volume threshold and decrease the frequency of contraction reflects.The MC counts in ileo-appendix and colon was reduced especially in colon and SP level in ileo-appendix and colon was degraded especially in colon after oral administration of IOFPP.Conclusions:adjustment to the secretion of MC and SP may be one of important mechanism of IOFPP

which can reduce the visceral hypersensitivity.