Objective To investigate the current situation of medication adherence of outpatients with depression / bipolar disorder， and explore the influencing factors of medication adherence. Methods A total of six 3A psychiatric hospitals or general hospitals， including Beijing Anding Hospital Affiliated to Capital Medical University， Nanjing Brain Hospital， the First Affiliated Hospital of Kunming Medical College， Guangzhou Psychiatric Hospital， the First Affiliated Hospital of Harbin Medical University and Xijing Hospital Affiliated to the Fourth Military Medical University， were selected as research centers by multicenter continuous enrollment. From October 2015 to March 2016， the outpatients with depression / bipolar disorder from every center were interviewed， and the medication compliance and related factors were statistically analyzed. Results A total of 1 206 valid data were collected， of which 758 cases（ 62.85%） had poor medication compliance， and the proportion of bipolar disorder and depression was 56.49%（ 296/524） and 67.74%（ 462/682） respectively. The differences between the two groups in age， education level， disease diagnosis， the number of attacks within 2 years， the course of the attack， the severity of depression， insight， and the type of hospital were statistically significant（ P＜ 0.05）. Multivariate analysis showed that the risk of non-compliance was lower in patients with bachelor degree or below（ OR=0.719， 95%CI： 0.542-0.953， P＜0.05）； the risk of non-compliance was lower in patients with 2 episodes with last 2 years（ OR=0.424， 95%CI： 0.251-0.716， P＜0.01）； the risk of non-compliance was lower in patients with moderate to severe depression（ OR=0.444， 95%CI： 0.327-0.603， P＜0.01）； the risk of non-compliance was lower in general hospital patients than in psychiatric hospital patients（ OR=0.328， 95%CI： 0.241-0.447， P＜ 0.01）； the risk of non-compliance was higher in depression patients than in bipolar disorder patients（ OR=1.659， 95%CI： 1.205-2.284， P＜0.01）. Conclusions The medication adherence of outpatients with major depressive disorder or bipolar disorder is not optimistic. The related factors include the type of disease， the severity of the current attack， the number of previous attacks， the type of hospital， and the level of education. It is necessary to take measures to improve the medication adherence of patients with depression and bipolar disorder.