There is currently no published clinical trial on the safety and effectiveness of aripiprazole in Taiwanese patients with treatment-refractory major depressive disorder. We were interested in determining the applicability of current recommended doses of aripiprazole as an adjunct to antidepressant therapy in this population. We conducted a prospective, open-label nonrandomized, 4-week flexibly dosed (2.5-5 mg/d) trial with aripiprazole augmentation in 9 Taiwanese patients who had a history of nonresponse to at least 2 adequate courses of antidepressant therapy with different types of antidepressants. The primary end point for clinical effectiveness was mean change in the 17-item Hamilton Rating Scale for Depression at the end of the 4-week trial. Secondary end points for clinical effectiveness included mean change in Beck Depression Inventory and Beck Anxiety Inventory scores. The Systematic Assessment of Treatment Emergent Events-General Inquiry was used to assess adverse effects. All patients completed the trial and responded to treatment; the remission rate was 77.8%. The mean daily dose of adjunctive aripiprazole was 4.2 mg. Common treatment-emergent adverse events included insomnia and sedation (33.3%) and akathisia (22.2%). We found high effectiveness despite a lower mean daily dose of adjunctive aripiprazole (4.2 mg) when compared with previously reported findings; however, we also observed a higher frequency of treatment-emergent adverse effects. Additional studies are required to ascertain whether there are ethnic differences in the pharmacokinetics and/or pharmacodynamics of aripiprazole in treatment-refractory depression.