Although many investigators have been searching for genetic markers to predict lithium response in bipolar disorders, no genetic predictor has been established yet. We previously reported the association of mitochondrial DNA (mtDNA) 5178 and 10398 polymorphisms with bipolar disorder. The objective of this study is to clarify whether these mtDNA polymorphisms can predict response to maintenance lithium treatment in bipolar patients. We examined these polymorphisms and some clinical variables in 54 bipolar patients. A logistic regression analysis was performed and revealed that patients carrying the 10398A polymorphism showed a significantly better response to lithium (p=0.03). Some clinical variables such as sex, age at onset, and rapid cycling also showed a significant association with lithium response in univariate analysis (chi2 test, p&0.05). Our findings suggest that the mtDNA 10398 polymorphism might be related to maintenance lithium treatment response.