Background of Study: Caries in the deciduous teeth is still a considerable problem in preschool age. World Health Organization (WHO) in 2003 stated that the incidence of dental caries in children is 60-90%. Caries in exclusive breastfeeding children caused by the child was breastfed during sleep, saliva production during sleep was reduced so that protection in the teeth decreased. Aim of Research: The aim of this research is to find out the relation between exclusive breastfeeding and dental caries severity level in 4-6 years old children. Research Methodology: This type of research is an analytic observational research with cross sectional design. The sample was taken with total sampling technique to 72 kindergartners. Caries severity level measured with Caries Severity Index (CSI) examination. The data analysis was using Mann Whitney test. Research Result: The research result shows that the 41 kindergartners consumed exclusive breastfeeding, while the 31 kindergartners are not consumed exclusive breastfeeding. The mean caries severity level in kindergartners with exclusive breastfeeding is 2,1. The mean caries severity level in kindergartners who are not with exclusive breastfeeding is 2,09. The result shows that (P > 0,05) so there are no relation between exclusive breastfeeding with dental caries severity levelin 4-6 years old children. Conclusion: There is no relation between exclusive breastfeeding with dental caries severity level in 4-6 years old children in Kasihan, Bantul.