Background. This study reports the prevalence of abnormal weight and associated characteristics of low-income Korean children. Methods. Health examination and survey were conducted nationally with 2033 low-income elementary students (mean age ± SD = 9.42 ± 1.65 years). Prevalence of abnormal weight and odds ratios (ORs) of health behaviors for abnormal weight groups were calculated. Results. Prevalence was 8% for underweight and 16% for overweight/obese. Compared with normal weight children, overweight/obese children were more likely to eat a variety of foods (OR = 1.82, P = .04) and have 3 meals a day (OR = 2.07, P = .047), but they were more likely to be stressed by their appearance (OR = 3.88, P < .001). Underweight children were less likely to have night snacks (OR = 0.28, P = .038) and more stressed by academic performance (OR = 3.76, P = .005) but were less educated about physical education (OR = 3.19, P = .044) and substance abuse (OR = 2.78, P = .018). Conclusion. Higher prevalence of abnormal weight among low-income Korean children calls for attention to address both childhood obesity and underweight in public health research and practice.