：Objective To investigatethe validity and reliability of the Chinese version Mood Disorder Questionnaire (C-MDQ) inthe patients with bipolar disorder (BP) and the optimal cutoff, sensitivity andspecificity using the C-MDQ to distinguish between the BP patients and patients with majordepression disorder (unipolar depression disorder, UP). Methods The English version MDQwas translated into Chinese version with consent of the author of the questionnaire. 284patients with BP and 134 with UP in outpatients and inpatients departments diagnosticallyinterviewed with DSM-Ⅳ were consecutively rated bythe C-MDQ. The test-retest reliability with interval of eight to fourteen days wasinvestigated in 147 BP patients (51.8%). Results A two-factor solution was preferred bythe factors analysis. The Eigenvalues of these two factors were 2.98, 2.14 respectively.The two factors together accounted for 39.4% of the total variance. The internalconsistency (Cronbach's alpha) of the C-MDQ was 0.77. The test-retest reliability of theC-MDQ was 0.63(P ＜0.01 ). The frequency of positive responses to various items ranged from 32.4% to78.2%. A C-MDQ screening score of 7 or more was chosen as the optimal cutoff between thepatients with BP and UP, as it provided good sensitivity (0.64) and nice specificity(0.80). Conclusions The study demonstrated the suitable validity and reliability of C-MDQ,suggesting that the C-MDQ is supplementary instrument to screen bipolar disorder in China,and 7 can be the cutoff when the C-MDQ used to discriminate between the BP and UP in thepatients with mood disorder in clinical practice.