Objectives: Purpose of this study is to analyze caries patterns of children aged under three years old in Taiwan.Materials and Methods: The research was conducted on children aged under three years old selected by stratified cluster sampling in Taiwan. The protocol of examination was based upon the criteria from WHO, and the data was analyzed for caries patterns.Results: Data of 665 children under three years of age were collected. The mandibular second primary molars were the most susceptible teeth in the primary dentition. According to the O'Sullivan's Caries Classification, the caries patterns are mainly ”restricted to maxillary anterior teeth”.Conclusions: The caries status of children under three years of age is still poor in Taiwan. Early caries prevention programs should start with children before tooth eruption.