The purpose of this study was to determine the effects of nutrient intake, screen time (television viewing and computer and/or video games) and physical activity on obesity in preschool children. Recruitment began in January 2008 by distributing letters to mothers who had children aged 6 years enrolled in daycare. Dietary intakes were obtained from the children's mothers, using the 24-hour recall method. The average height and weight of the children were 114.2 cm and 20.3 kg, respectively. Mean age, body weight, height and Kaup index were not significantly different between groups consisting of boys or girls. Assessment by the Kaup index showed that 14.0% of children were underweight, 69.0% were normal weight, 13.0% were overweight, and 4% were obese. The daily intakes of calcium, potassium, fiber, and folic acid in the group of boys were 77.7%, 58.5%, 80.4% and 88.9% respectively. as compared with the DRIs. The daily intakes of calcium, potassium, fiber, and folic acid in the group of girls were 77.7%, 58.5%, 80.4% and 88.9%, respectively. as compared with the DRIs. Intakes of protein, phosphorus, iron, zinc, vitamin A, thiamin, riboflavin, niacin, vitamin C, and vitamin E were higher than the DRIs. There were no difference among 3 groups (underweight, normal, overweight) in energy or nutrient intake. Preschool children with screen time (TV viewing and computer and/or video games use time) of >2 hours per day had significantly higher Kaup index values, and intakes of energy, carbohydrate, folic acid and zinc. In conclusion, preschool children with reported screen time (TV viewing and computer and/or video games use time) of >2 hours per day were fatter. Therefore, we need further investigate the relation between diet and screen time in preschool children to improve future nutrition education programs. Further studies are required to explore the effects of food intake and screen time (TV viewing and computer and/or video games use time) over a longer period of time.