Bipolar disorder is a kind of serious mental disease. Bipolar disorder occurs as depression in most cases, which may result in the misdiagnosis as unipolar depression, delayed therapy and unfavorable prognosis. Therefore, the early diagnosis of bipolar disorder is very important. The pathogenesis of bipolar depression is extremely complicated, which concerns with numerous fields. However, few studies have focused on the specific molecular biomarkers in bipolar depression. This review is to introduce the research progress of early diagnosis of bipolar disorder on the fields of genetics, neuroendocrine and biochemistry, discussing the molecular biomarkers which may contribute to the early diagnosis of bipolar disorder.