Introduction: Despite theavailability of numerous antidepressant drugs the therapy of depression is far from satisfactory. Two of the many reasons for this are the delay in onset of effect and the adverse effects associated with most of the antidepressants. Costus speciosus rhizome has shown adaptogenic activity. Objective: To evaluate the antidepressant activity of50% aqueous-ethanol extract of Costus speciosus (CS) leaves in experimental models of depression. Materials and Methods: Male albino mice were randomly assigned to five groups of six each. We studied three doses of the leaf extract (100, 200 and 400 mg/kg) on two models of depression -forced swim test and tail suspension test. Imipramine was used as the standard control. Both acute and chronic effects were studied. Drugs (test drug, standard control and vehicle) were administeredorally, one hour before the experiment in the acute study and daily for 14 days for the chronic study. Results: Imipramine showed significant antidepressant activity as demonstrated by a reduction in duration of immobility in both acute and chronic studies of forced swim test and tail suspension test. CS showed a dose dependent antidepressant activity. CS_100 demonstrated an antide-