Objective: To investigate the prevalence of affective disorder in Kunming City. Methods: A rep-resentative sample of the Kunming general population composed of 5033 individuals aged 15 years and older was se-lecteed randomly by the method of probability proportional to size (PPS), and then was interviewed with the World Health Organization Composite International Diagnostic Interview Version 2.1 (CIDI, version 2.1).The preva-lence of affective disorder was investigated. And the relative factors, onset age and comorbid were also analyzed. Results: The 30-duy prevalence of affective disorder was 0.98%, the 12-month prevalence was 1.22%,and the lifetime prevalence was 1.89%. The results of the single factor analysis showed that the urban residents, the persons who divorced, limited divorced or lost one's spouse, and the unemployed or the higher educated were more vulnerable to depression. The results of the multifactor analysis showed that the rural residents and the males were protective factors to affective disorder. Different subunits of affective disorder had different onset ages. The onset age of 90% bipolar disorder patients was before 25 years old. The patients before 50 years old was risky to dysthy-mia. The patients with major depression had a lifetime risk of onset. Anxiety disorder and pain disorder would in-crease the risk of affective disorder. Conclusion: The findings show that the prevalence of the affective disorder is lower than the same kind survey abroad while it is close to the domestic's. More attention and intervention should been given to the urban population, the females, the singles, the unemployed, and the higher educationed.