To examine the differences in depressive state and associated factors between informal and professional caregivers, a cross-sectional study was carried out in 23 informal home-based caregivers of demented patients, 24 professional caregivers working in the dementia ward of a psychiatric hospital, and 31 controls. Measurements included severity of dementia (Clinical Dementia Rating Scale, Mini Mental State Examination, MMSE) and levels of caregivers depression (Beck Depression Inventory; BDI), care burden (Zarit Caregiver Burden Interview; ZBI) and quality of life (World Health Organization-Quality of Life-26, WHO-QOL26). Informal caregivers had the highest BDI score and ZBI and the lowest QOL among the three studied groups. Regarding informal caregivers, there was a strong positive correlation between BDI and ZBI scores. The BDI and ZBI scores were significantly high when patients exhibited behavioral problems. The four WHO-QOL categories (physical domain, psychological domain, social relationships and environment) had a strong negative correlation with BDI. Regression analysis demonstrated that the psychological domain points of WHO-QOL, role strain factor of ZBI and MMSE score were significantly associated with BDI. Regarding professional caregivers, their BDI score had a strong negative correlation with the physical and psychological domains and environment categories of WHO-QOL. Regression analysis demonstrated that their BDI score was significantly associated with the psychological domain and environment. It is thus very important to provide sufficient social care services and/or personal support to informal caregivers.