Objective:To evaluate the antidiarrhoeal property of methanol extract of the leaves of Rauwolfia serpentina (R. serpentina) in experimental diarrhoea induced by castor oil in mice. Methods:Doses of 100, 200 and 400 mg/kg R. serpentina leaf methanol extracts were administered to castor oil induced diarrhoea mice to determine its antidiarrhoeal activity. Results: All doses of the extract and the reference drug atropine sulphate (3 mg/kg, i.p.) produced a dose-dependent reduction in intestinal weight and fluid volume. The extracts also significantly reduced the intestinal transit in charcoal meal test when compared to diphenoxylate Hcl (5 mg/kg, p.o.). Conclusions: The results show that the extract of R. serpentina leaves has a significant antidiarrhoeal activity and supports its traditional uses in herbal medicine.