No study has directly compared the efficacy and tolerability of aripiprazole augmentation (AA) and antidepressant switching (SW) in patients with major depressive disorder (MDD). This is the first 6-week, randomized, rater-blinded, direct comparison study between AA and SW in outpatients. An inadequate response to antidepressants was defined as a total score ≥ 14 on the Hamilton Depression Rating Scale-item 17 (HDRS-17) despite adequate antidepressant dosage for at least 6 weeks in the current depressive episode. The primary endpoint was change in the total score of the Montgomery-Åsberg Depression Rating Scale (MADRS) from baseline to the end of treatment. Secondary efficacy measures included the response and remission rates as priori defined at the end of treatment: changes in total scores of the HDRS-17, Iowa Fatigue Scale (IFS), and Sheehan Disability Scale (SDS) from baseline to the end of treatment and the proportion of patients who scored 1 or 2 on the Clinical Global Impression-Improvement Score (CGI-I) at the end of treatment. Tolerability was assessed with the Barnes Akathisia Rating Scale (BARS) and Arizona Sexual dysfunction scale (ASEX), and the numbers of adverse events were compared between the two groups. A total of 101 patients were randomized to either AA (n = 52) or SW (n = 49). The mean change in the MADRS score from baseline was significantly higher in the AA, with a difference in magnitude of -8.7 (p < 0.0001). The intergroup difference was first evident in week 2. The numbers of responders (p = 0.0086) and remitters (p = 0.0005) were also significantly higher in the AA (60% and 54%, respectively) compared with the SW (32.6% and 19.6%, respectively). On most secondary endpoints, AA showed better clinical outcomes compared to SW. The tolerability profiles were comparable between the two groups. Overall, AA yielded potentially beneficial clinical outcomes compared to SW. Given the methodological shortcomings of the present study, adequately powered, more rigorously controlled clinical trials are strongly warranted to confirm the present findings.