This paper is aimed to review the applications and potentials of QEEG in early diagnosis of bipolar disorders as well as its diagnostic efficacy for differential diagnosis against other cognitive abnormalities with the same clinical symptoms. The databases of PubMed (1990-2016), EMBASE (1990-2016), Web of Sciences (1990-2016), and Google Scholar (1980-2016) were searched using the search terms of "quantitative electroencephalogram" or "QEEG", "bipolar disorders", "early diagnosis", and "differential diagnosis". selected for further evaluations. The evidence indicates diagnostic efficacy of QEEG for early diagnosis of bipolar disorders (BDs). Controlled clinical studies have indicated that QEEG extracted measures may have the same diagnostic value for early and differential diagnosis of BDs as these conventional assessments.