BACKGROUND: Although the optimal duration of breastfeeding remains unclear, breastfeeding is generally recommended exclusively for the first 6 months of life, which continues into late infancy. However, the awareness regarding the effects of long-term breastfeeding is relatively low compared with that of breastfeeding in early infancy. We aimed to investigate the growth and nutritional characteristics of the children with prolonged breastfeeding (PBF) over 1 year. METHODS: This cross-sectional study was based on the data of children aged 12 to 23 months from the National Health and Nutrition Examination Survey (2010-2020) conducted by the Korean Center for Disease Control and Prevention. Data on anthropometric measurements, dietary behavior, and food and nutrient intake were extracted, and the association between PBF and growth, nutritional status, and dietary patterns were analyzed. RESULTS: Of the 872 children with a birth weight of ≥ 2.5 kg in the final analysis, 34.2% continued breastfeeding over 12 months of age, and their median breastfeeding duration was 14.2 months. Children with PBF were more likely to have lower current body weight (P < 0.001) and weight gain (P < 0.001), lower daily protein (P = 0.012), calcium (P < 0.001), and iron (P < 0.001) intake per calorie compared with children weaned by 12 months of age or those who were never breastfed. Furthermore, they were started on complementary food at 6 months or later rather than 4-5 months (P < 0.001), consumed cow's milk earlier (P = 0.012), and consumed probiotics as dietary supplements (P < 0.001) significantly less commonly. When comparing the intake of food groups, children with PBF had a significantly higher intake of cereals and grains (P = 0.023) and fruits (P = 0.020) and a significantly lower intake of bean products (P = 0.020) and milk and dairy products (P = 0.003). CONCLUSION: Korean children who continued breastfeeding over 12 months of age showed distinct characteristics in terms of growth, nutritional status, and dietary patterns in the second year of life compared to children who did not. Long-term additional research on their growth and nutritional status may be needed; however, these findings are significant as important fundamental data for nutritional counseling to establish healthy PBF.