Objective: Purpose of this study is to review the studies investigating the efficacy and tolerability of extended-release quetiapine (quetiapine XR) as adjunctive therapy and monotherapy in major depressive disorder. Method: Nine articles were reviewed that were reached after the search in Medline/pubmed search engine by using "quetiapine XR", "depression", "anxiety" key words. The search was done in March 2011. The reviewed articles were published between 2009 and 2011. Results: In studies that investigate the efficacy of quetiapine XR as adjunctive therapy remission rates were found between 31%-42.5%. Remission rates were found between 20.8%-34.7% in studies that investigate the efficacy of quetiapine XR monotherapy. Studies showed that MADRS total scores were significantly reduced compared to placebo at week 1. Satistically significant improvements were seen in HAM-D total, HAM-A total, and HAM-A psychic anxiety cluster scores. Besides reducing depressive symptoms, quetiapine XR is also significantly effective in anxiety symptoms compared to placebo. Conclusion: Because of significant effectiveness, high tolerability rates, quetiapine XR emerges as a new treatment option in patients with major depressive disorder with an inadequate response, treatment resistance, concomitant anxiety symptoms. Moreover significant improvement in inner tension, reduced sleep, pessimistic thoughts as early as week 1 is clinically important