A cross-sectional study was conducted to examine the nutritional status of children (aged 1-5 years) who lived in the Klong Toey slum, Bangkok; the factors related to nutritional status were also determined. Anthropometric measurements were made for 232 children; socioeconomic background information was obtained by interviewing their mothers using a structured questionnaire. The prevalence of malnutrition among the study sample was 25.4% by weight-forage, 18.1% by height-for-age, and 6.9% by weight-for-height; the prevalence among pre-school children in Thailand and in the Bangkok metropolitan area by weight-for-age was reported to be 8.73% and 5.25% respectively. Potential related factors were examined: family characteristics, (mother's age, marital status, educational background, family size, family income, and mothers' occupation); children's characteristics (age, gender, birth order, immunization status, and history of illness); mothers' knowledge and perception of nutrition and mothers' food practice. Multiple logistic regression analysis was used to identify the association with the nutritional status of children by height-for-age. The results showed that family income (adjusted OR=0.9998; 95% CI: 0.9997-1.0000), maternal housewifery or unemployment (adjusted OR=6.5; 95% CI: 1.74-24.3), food practice (adjusted OR=0.7123; 95% CI: 0.5390-0.9414), and a maternal educational level lower than primary school (adjusted OR=10.1; 95% CI: 1.13-91.9) were associated with the nutritional status of children. This finding implies that although malnutrition is no longer considered to be a major health problem in Thailand, it remains a threat to the health of the urban poor in Bangkok. This finding should not be overlooked and countermeasures are indicated.