With the rapid development of neuroimaging in recent years, increasing evidences indicate that there are alterations of brain structure and function in patients with major depressive disorder. As an important region in limbic system, hippocampus is relevant to abnormal emotional regulation and cognitive impairment. This paper reviews the research advances of structure and functional magnetic resonance imaging of hippocampus of patients with major depressive disorder and discusses the biological mechanisms of hippocampus of patients with major depressive disorder.