Background: Depression and anxiety disorders are considered to be among the greatest burdens of disease in children and adolescents. Recent literature has reported music therapy to be a safe and potentially effective intervention for the treatment of depression and anxiety. This systematic review examined the effectiveness of music therapy in reducing the symptom severity of depression and/or anxiety among children and adolescents. Methods: Randomized controlled trials (RCTs) were obtained from a systematic search of nine major English databases from inception to January 2021. Studies were categorized by outcome, music therapy technique and follow-up period. Results: Seven RCTs (n = 589) were included. Four RCTs had some concern of bias, while three had high risk of bias. Statistical pooling was not appropriate due to clinical heterogeneity. Four studies (n = 428) favoured music therapy for improvement of depressive symptoms at short- and intermediate-term follow-ups compared to control. One study (n = 106) favoured music therapy for improvement of anxiety symptoms at short-term follow-up compared to control. No studies favoured any control over music therapy for symptom improvement of depression and/or anxiety. Conclusion: Limited evidence suggests music therapy is an effective treatment for improving depression and/or anxiety symptom severity in children and adolescents. More high-quality RCTs are needed to address methodological flaws of current studies. Keywords: Music; adolescence; anxiety; depression; therapy.