Objectives:The objective of this study was to explore the explanatory factors on the length of stay of psychiatric patients in various mental health-related facilities. Methods:Subjects in this study were consisted of 1,028 psychiatric patients staying in 22 mental health-related facilities randomly sampled after proportional stratification by regions. The subjects in 22 mental health-related facilities including psychiatric hospitals/clinics, psychiatric welfare facilities, welfare facilities for homeless, and illegal institutions were interviewed by psychiatrists and social workers with clinical experience. Demographic characteristics, socioeconomic support,diagnosis/history of illness, clinical symptom/functional disability and type of facilities were investigated and included in the multiple regression models to examine their influence on the length of stay. Results:Two thirds of total variance of length of stay were explained by the independent variables in this study, and the type of facilities had the most explanatory power. In addition to type of facilities, sex, age, economic status, type of medical security, familial support, living condition before admission, diagnosis, dual diagnosis, age of onset of illness and number of admissions were significant explanatory factors. Conclusion:This study provides bases for specific strategies to develop efficient mental health facilities and community mental health system by disclosing the important explanatory factors for length of stay.