Abstract: Clonidine (15～120μg/kg, sc) showed a dose related inhibitory effect on the gastrointestinal propulsive motility in mice and rats, and on the defecation in mice. This action of clonidine was much stronger than that of morphine. No tolerance to the action of clonidine was observed on repeated administration of the drug (120 μg/kg·d×10 d). Clonidine (12μg/kg, icv) was found to be more active in inhibiting the gastrointestinal propulsive motility than the same dose of the drug given sc. Yohimbine (0.5～5 mg/kg, sc) exhibited an antagonistic action on the inhibitory effect of clonidine on the gastrointestinal propulsion and defecation in mice.