The principal objective of this study was to determine the effects of mothers' nutrition knowledge on preschoolers' obesity and dietary habits. The subject population included 456 mothers and their preschoolers, aged 3 to 5 years, who were enrolling in kindergartens located in Seoul and KyongGi-Do, Korea. The results of this study are as follows: 1. The majority of mothers responded correctly to those questions concerning obesity-related nutritional knowledge, but responded incorrectly to questions regarding basic nutritional knowledge. 2. The mothers' nutritional knowledge was associated significantly with the mother's age (p<0.05) and degree of education (p<0.05). 3. The mothers' nutritional knowledge was significantly and negatively correlated with their obesity, but not with their preschoolers' obesity. 4. Mothers' nutritional knowledge was determined to be positively associated with higher interest in nutritional information and food selection in regard to weight management strategies for their kids. 5. In general, preschoolers whose mother had excellent nutrition knowledge evidenced better dietary habits than preschoolers whose mothers had poor nutrition knowledge. In particular, one question regarding serving size was significantly associated with mothers' general level of nutritional knowledge(p<0.05).