Depression is an important health problem in children and the onset of depression is occurring at a younger age than previously suggested. The associations of being overweight and low socioeconomic status in childhood de- pression have been well documented; nevertheless few studies have addressed the combined effects of socioeconomic status and body weight, with depression in school-age children. We intended to examine if the relation- ship between socioeconomic status and childhood depression could be modified by abnormal body weight. A cross-sectional study was performed with a total of 559 subjects from 29 elementary schools in Taiwan. A de- pression scale was used to determine the depression status. Children receiving governmental monetary assistance for after-school class were categorized as being in the lower socioeconomic group. Data for depression-related demographic characteristics, family and school variables were collected. Children in the lower socioeconomic status group have a higher prevalence of depression (23.5%) than those in higher socioeconomic status groups(16.4%). Being overweight demonstrates the opposite effect on depression risk in the different socioeconomic groups. In lower socioeconomic families, the risk of depression in overweight children is three times higher than that for normal weight children; whereas in higher socioeconomic families, overweight children have a lower risk for depression than normal weight children. We concluded that a qualitative interactive effect existed between being overweight and socioeconomic status with childhood depression. More attention should be paid to overweight children from lower socioeconomic status families to prevent depression in school-age children.