Several secondary metabolites have been isolated from Zornia brasiliensis (Leguminosae), mainly flavonoids. These compounds are known for many pharmacological actions, such as antispasmodic and antidiarrheal. Therefore, we evaluated the antidiarrheal effect of the ethanolic extract obtained from Zornia brasiliensis aerial parts (ZB-EtOHAP), as well as its underlying mechanisms. Castor-oil-induced diarrhea, fluid accumulation, and intestinal transit (normal and castor oil induced) were performed to assess the antidiarrheal, antisecretory, and antipropulsive activities of the extract. The involvement of opioid and adrenergic pathways was also investigated. ZB-EtOHAP inhibited, in a dose-dependent manner, both total defecation frequency and the number of watery stools. The extract showed no effect on fluid accumulation or normal intestinal transit. On the other hand, when the animals were pretreated with castor oil, the extract decreased the distance traveled by the marker in the small intestine. Investigation of the involvement of opioid and adrenergic systems showed that the pharmacological potency of the extract did not change in the presence of naloxone, but it was reduced in the presence of yohimbine. The data indicate that Zornia brasiliensis has an antidiarrheal effect due to inhibition of the intestinal motility through adrenergic pathway activation.