Myakuryu (MR) is a newly developed herbal medicine composing Crataegue oinnatifida bge (COB), Panax notoginseng (PN) and Ginkyo biloba (GB). To examine the effectiveness of MR, we investigated its effects on rat mesenteric microcirculatory injury induced by ischemia/reperfusion (I/R). The mesenteric microcirculation of ileocecal portion of a male Wistar rat was observed through an inverted-type intravital microscope assisted with a charge-coupled devise (CCD) camera. Mesenteric I/R was conducted by a ligation of the mesenteric artery and vein (10 min) and subsequent release of the occlusion. We measured venular diameter, the number of adherent leukocytes, dihydrorhodamine 123 (DHR) fluorescence as an indicator of oxidative stress and mast cell degranulation, with or without MR extract (0.4 g/kg b.w.) via an orogastric tube 1 hr before I/R. The diameters of the observed mesenteric venules were not changed after the mesenteric I/R. MR had no effect on venular diameter. The leukocytes adhering to the post-capillary venular walls started just after reperfusion, and increased thereafter. The increased number of adherent leukocytes was significantly reduced by treatment with MR. DHR fluorescence ratio was significantly increased along the venular wall. MR attenuated the increased oxidation. The mesenteric I/R induced mast cell degranulation. The increase in mast cell degranulation was inhibited by MR. In conclusion, oral administration of MR attenuates I/R-induced microvascular damages in rat mesentery. MR has a therapeutic potential for prevention of I/R-related microvascular injury.