Objective: Several evidence-based practice guidelines have been developed to better treat bipolar disorder. However, the articles cited in these guidelines were based on clinical or basic studies with specific conditional settings and were not sufficiently based on real-world clinical practice. In particular, there was little information on the doses of mood stabilizers. Methods: The MUlticenter treatment SUrvey on BIpolar disorder in Japanese psychiatric clinics (MUSUBI) is a study conducted to accumulate evidence on the real-world practical treatment of bipolar disorder. The questionnaire included patient characteristics such as comorbidities, mental status, treatment period, Global Assessment of Functioning (GAF) score, and details of pharmacological treatment. Results: Most patients received mood stabilizers such as lithium (n = 1,317), valproic acid (n = 808), carbamazepine (n = 136), and lamotrigine (n = 665). The dose of lithium was correlated with age, body weight, number of episodes, depression and GAF. The dose of valproic acid was correlated with body weight, number of episodes, presence of a rapid cycle and GAF. The dose of carbamazepine was correlated with age, mania, and the presence of a rapid cycle. The dose of lamotrigine was correlated with the number of episodes, depression, mania, psychotic features, and the presence of a rapid cycle. Doses of coadministered mood stabilizers were significantly correlated, except for the combination of valproic acid and lamotrigine. Conclusion The dose of mood stabilizers was selectively administered based on several factors, such as age, body composition, current mood status and functioning. Further prospective studies are required to confirm these findings.