Exosomes are a type of membrane-bound vesicles that carry various information molecules such as miRNAs. They are stable in various surrounding body fluids and can cross the blood-brain barrier, making them an ideal source of biomarkers for clinical disease diagnosis and therapeutic evaluation. Bipolar Disorder (BD) is a severe mental disorder characterized by recurrent episodes of mania and depression. Currently, the diagnosis and efficacy assessment of BD mainly rely on clinical interviews and observations, and there is a lack of clear biomarkers and effective laboratory testing methods. In recent years, increasing evidence showed an imbalanced expression pattern of plasma exosomes miRNA in BD patients, with a close correlation with the clinical phenotype, disease progression, and treatment response. Results of the preliminary mechanism research indicated that the extracellular miRNAs may participate in the occurrence and development of BD by regulating target genes and signaling pathways. However, there are still some limitations and challenges in the current research on extracellular miRNAs in BD. Further improvement and standardization are needed. This article reviews the role of extracellular miRNAs in the pathogenesis of BD and their potential as biomarkers for the diagnosis and treatment. By comparing the expression profiles of extracellular miRNAs in BD patients with other mental disorders or neurodegenerative diseases, their potential applications in cross disease diagnosis and treatment are evaluated.