Objective：To investigate the associations of major depressive disorder with coronary heart disease (CHD) and stroke in Chinese adults aged 30-79 years. Methods:In 2004－2008, China Kadoorie Biobank was conducted in 10 geographically defined regions (5 urban and 5 rural) of China. A total number of 512 891 participants aged 30-79 years were recruited in the baseline survey. A laptop-based electronic questionnaire was administrated face-to-face by trained health workers, collecting the general demographic and socio-economic status, dietary and other lifestyle behaviours (e.g. smoking, alcohol drinking, physical activity), medical history and family history of common chronic diseases. Major depressive episodes (MDE) in the past 12 months were assessed with the World Health Organization composite international diagnostic interview-short form (CIDI-SF). The physical measurements included the heights and weights, which were used to calculate the body mass indexes (BMI).Chi squared and t test were used to compare the differences in participants characteristics according to their major depressive disorder. Logistic models were employed to estimate the odds ratios (OR) and 95% CI of their major depressive disorder with prevalent coronary heart disease and stroke.Results: Among the 512 891 participants, 3 281 (0.6%) showed an MDE in the preceding 12 months, 15 472 (3.0%) reported prevalent CHD, and 8 884 (1.7%) reported prevalent stroke. Major depressive disorder was significantly associa-ted with an increased risk of CHD and risk of stroke. Age-and gender-adjusted ORs (95% CI) were 1.80 (1.53－2.12) for CHD and 2.53 (2.09－3.05) for stroke. The associations were significant after further adjustment for potential confounders, such as other socio-demographic status, smoking, alcohol drinking, physical activity, and BMI, prevalent hypertension, diabetes as well as family history of cardiovascular diseases (OR=1.83, 95% CI=1.54－2.18 for CHD; OR=2.19, 95% CI=1.79－2.69 for stroke). Moreover, gender significantly interacted with MDE on prevalent stroke (P for multiplicative interaction=0.013). The men with an MDE in the past 12 months had the highest risk of stroke in the joint analyses of gender and depression disorder (OR=5.02, 95% CI=3.70－6.82). Conclusion:The findings from this large crosssectional study suggest that the presence of MDE is a risk factor for both CHD and stroke in Chinese adults aged 30－79 years, but further prospective studies are warranted to validate the results.