ObjectiveTo investigate the effect of porcine large intestine-processed Dahuang （Radix et Rhizoma Rhei） on defecation in constipation model mice and the possible mechanism. MethodsFifty Kunming mice were randomized to blank group （n=10） and model group （n=40）. Loperamide suspension at the dose of 8 mg/（kg·d） was given by gavage for four consecutive days to establish a model of constipation. The 24 successfully modeled mice were randomly divided into model group， processed Dahuang group， lactulose group， raw Dahuang group， with six mice in each group. Moreover， six randomly selected mice were chosen as control group. Since the fifth day， 8 mg/（kg·d） of loperamide suspension by gavage was given to the model group， processed Dahuang group， raw Dahuang group， and lactulose group； two hours later， the processed and raw Dahuang groups were administered with 0.6 g/（kg·d） of processed and raw Dahuang suspension， respectively， while the lactulose group was given 0.6 g/（kg·d） of latulose suspension， and the blank group and the model group were given 0.2 ml/10 g of distilled water by gavage， all for four days. The general condition， body weight after the last gavage， number of fecal particles within six hours， fecal wet weight， fecal water content ratio， intestinal propulsion rate and colonic histology changes by HE staining of each group were detected. ResultsThe body weight of the mice in the raw Dahuang group was significantly lighter than that in the other groups （P＜0.05 or P＜0.01）. The number of fecal particles， fecal wet weight and intestinal propulsion rate of mice significantly decreased in the model group than in the blank group （P＜0.05 or P＜0.01）. Compared to those in the model group， the number of fecal particles and fecal wet weight in the processed Dahuang group， lactulose group and raw Dahuang group significantly increased， and the fecal water content ratio in the raw Dahuang group increased as well （P＜0.05 or P＜0.01）. Compared to those in the processed Dahuang group， the number of fecal particles and fecal wet weight in the raw Dahuang group decreased， while the fecal water content ratio increased （P＜0.05 or P＜0.01）， and the fecal water content ratio in the lactulose group increased significantly （P＜0.05）. The intestinal propulsion rate in the processed Dahuang group was higher than that in the model group， lactulose group and raw Dahuang group （P＜0.05 or P＜0.01）. Histopathological analysis showed that the colonic crypts and goblet cells in the blank group were normal and clear， and the colonic muscular layer was thicker. The colonic crypts of the mice in the model group were damaged， with reduced goblet cells to varying degrees and changed colonic muscularis. In the lactulose group and raw Dahuang group， part of the crypts were broken， and the goblet cells were damaged to varying degrees， while in the processed Dahuang group， still the colonic tissue structure of the mice was relatively clear， and the colonic crypts and goblet cells were relatively normal， with thickened muscular layer of the colon. ConclusionPorcine large intestine-processed Dahuang could improve defecation in constipation model mice， and reduce the drastic purgation function of raw Dahuang， for which the mechanism may be related to the protection of colon histopathological damage.