Abstract Background Obesity is a serious worldwide public health problem, especially for people with mental disorders. Aim To explore the related factors of obesity by analyzing the metabolic indexes of patients with common mental disorders in stable stage. Methods Five hundred seventy-six subjects with major depressive disorder (MDD), bipolar disorder (BD) or schizophrenia (SCZ) were included, who received fixed drug dose and routine drug treatment for 2 years or more. Their venous blood was collected, and the blood metabolic indexes were analyzed. Results BD and SCZ are more prone to obesity than MDD. Multiple linear regression analysis showed that the value of BMI increased with the increase of age(B = 0.084, p