BackgroundThis study aims to investigate the association between malnutrition and early childhood caries (ECC) and caries activity among children aged 3–5 years, in order to provide a theoretical basis for preventing and blocking ECC and improving malnutrition.MethodsChildren aged 3–5 years from six kindergartens in Zhao Xian, China were enrolled in this study. The decayed, missing, filled teeth (dmft) of all children were examined and recorded. The Cariostat method was used to detect dental caries activity, collect anthropometric data and measure haemoglobin concentration. Parents were asked to complete a questionnaire on the general characteristics and oral health behaviour of the participants. The “Growth Standards for Chinese Children Under 7 Years Old” was used to assess the nutritional status of all participating children. Wilcoxon rank sum test and multivariate logistic regression analysis were used to analyse and evaluate the relationship between ECC, caries activity and malnutrition.ResultsA total of 635 children who met the criteria were included in this study. After adjusting for confounding factors, logistic regression showed that the risk of ECC was significantly increased in underweight children compared with normal children (OR = 5.43, P < 0. 05); compared with normal children, the risk of ECC decreased in overweight and obese children (OR = 0.31, P < 0.001); underweight children had higher caries severity than normal weight children, and the difference was statistically significant (OR = 2.69, P < 0. 05); stunted children had higher caries severity than normal weight children and the difference was statistically significant (OR = 2.28, P < 0.05); underweight was positively associated with caries activity and the association was statistically significant (OR = 2.33, P < 0. 05); stunting was positively associated with caries activity and the association was statistically significant (OR = 2.1, P < 0.05); overweight and obesity were negatively associated with caries activity and the association was statistically significant (OR = 0.61, P < 0.05).ConclusionsThe risk of ECC among children aged 3–5 years was positively associated with undernutrition and negatively associated with overnutrition. The severity of ECC among children aged 3–5 years was positively associated with undernutrition. The caries activity among children aged 3–5 years was positively associated with undernutrition and negatively associated with overnutrition.