Objective · To investigate the effects of simo decoction combined with mannitol on the intestinal preparation of magnetically guided capsule endoscopy (MGCE). Methods · A total of 120 patients were enrolled in this randomized controlled trial and randomly divided into two groups according to the random number table. The observation group (n=60) was pretreated with simo decoction 20 mL each time, 3 times a day combined with mannitol 500 mL for oral administration before MGCE examination, while control group (n=60) only was done with mannitol 500 mL for oral administration. Then the intestinal cleanliness and occurrence of adverse reaction were observed. Results · The intestine bubbles in observation group were less than that of control group based on evaluation criteria (Z=-1.976, P=0.048), and the intestine juices in observation group were also less than control group (Z=-2.489,P=0.013) suggesting that the intestinal cleanliness in observation group was superior to control group. Simultaneously, the score of nausea and vomiting in observation group was lower than control group according to the evaluation criteria (Z=-2.215, P=0.027), and abdominal pain, distension and anal stenosis in observation group were less than control group (Z=-2.158, P=0.031), meanwhile, the overall incidences of adverse reaction were 8.33% and 36.67%, respectively (χ2=13.811, P=0.000) , all of which implied that the occurrence of adverse reaction was lower in observation group compared to control group. Conclusion · Simo decoction combined with mannitol could enhance intestinal cleanliness and reduce the occurrence of adverse reaction so as to improve the effect of intestinal preparation.