Objective: Thymus algeriensis (Lamiaceae) used in Moroccan popular medicine has been investigated for its antidiarrheal effects.Methods: Antidiarrheal effects of the aerial-part Thymus algeriensis aqueous extract was carried out by using two standard methods of bioassay: Castor oil-induced diarrhea and gastrointestinal transit test.Results: The pre-treatment of rats with the 50 mg/Kg aqueous extract produced a significant inhibition against castor oil induced-diarrhea and fecal output; furthermore the extract significantly decreased the propulsive movement of the charcoal meal in the mice small intestines. The extract when administered at higher doses (100 and 200 mg/kg) caused increased peristalsis in charcoal fed animals and exhibited a less significant reduction in fecal output and castor oil-induced diarrheas than 50 mg/ml dose.Conclusion: The antidiarrheal effects of the extract may explain the rationale for the use of the plant in traditional medicine as a popular antidiarrheal recipe.Â