Although there has been a significant increase in breast-feeding (BF) rate in Korea, it is plateaued since 2008 and still low compared with that of other countries. Because BF has been related to lower obesity prevalence in many studies and the increase in childhood obesity became evident in Korea, we wondered if a relatively lower BF rate has anything to do with this increase. Therefore, we looked into the relationship between mode & duration of BF during infancy and weight status of toddlers using the data from Korea National Health and Nutrition Examination Survey 2008 through 2011. Number of 2-3 year old toddlers with complete information on BF, anthropometry and normal birth weight was 674. While 87% of them were ever-breastfed, 6.2% each of them were either obese or overweight based on the Standard Growth Chart for Korean Children. Not only the obesity prevalence was different among groups of different mode of feeding, but also the mean duration of BF was significantly longer in normal weight group (9.2 mo.) compared with obese group (5.5 mo.). Accordingly, overweight and obesity prevalence of the toddlers breast-fed for 12 months or longer was significantly lower than that of the toddlers breast-fed for less than 12 months (OR 0.53, 95% CI 0.32-0.87). This study revealed that both BF and duration of BF affect the childhood obesity and, BF for 12 months or longer should be encouraged more aggressively as one of the main strategies to prevent and/or decrease childhood obesity in Korea.