The prevalence and severity of caries in children under three years old are constantly increasing. One of the cause is the increase consumption of cariogenic carbohydrate. Breast milk have buffer capacity that eventually able to prevent caries. The aims of this research are to discover the correlation between breastfeeding with the severity of Early Childhood Caries (ECC) in children under three years old, to provide information on prevalence and severity of caries in children under three years, and to explain factors influencing the incidence of ECC. This research designed cross sectionally and conducted upon 565 children aged 12-38 months, selected using multistage cluster random sampling. The ECC prevalence of children under three years in DKI Jakarta is 52.7%, with average score of def-t 2.85. Bivariate analysis showed that, variables which correlate with the level of ECC are; the way to deliver (p=0,012), frequency (p=0,002), duration (p=0,002), salivary buffer capacity (p=0.013), habitual consumption of sugary diet (p=0.005), child?s dental hygiene behavior (p=0.002), and mother?s education (p=0.001). Multivariate analysis showed that ECC can be explained by these variables: age, mother?s education, the way to deliver and frequency of breast milk complements/replacement of consumtions, child?s brushing habit, plaque pH, and salivary buffer capacity. Resulting determination coefficient 32.1%. There is no significant correlation between breastfeeding and the level of Early Childhood Caries (ECC). The role of protective qualities of breastfeeding are not shown because of bias in obtaining data influence the incidence of caries.