Background and objectiveMalnutrition, pain, and insomnia are common adverse effects of early dental caries among 3–6-year-old children. To increase our understanding of the dental caries status which will help in the control and prevention of it, this study aimed to assess the trend of dental caries, Severe Early Childhood Caries (S-ECC) and its related factors among 3–6-year-old children during a 9-year period in Babol, Northern Iran.MethodsThis was a cross-sectional study among 2,080 children aged 3–6 years old in Babol, Northern Iran. The studied samples were examined from May 2007 to June 2015. Oral examinations were performed with visual-touch technique. S-ECC was measured as number of decayed, missing, and filled teeth surface (dmfs). Data were evaluated by SPSS software for Windows version 23 and were analyzed using the one-way ANOVA, chi-square test and independent-samples t-test. Level of significance was set at ≤ 0.05.ResultsThe trend of dental caries and S-ECC rose among 3–6-year-old children over a 9-year period. Of the children, 26.3% were caries free. The mean dmft was increased significantly among boys (p<0.001), among 3–4-year-old children (p=0.01), and those children with both employed parents (p=0.01) and low educated parents (p<0.001) from 2007 to 2015.ConclusionDental caries status showed an increasing trend over the study period in Babol preschool children, therefore effective preventive strategies are required to decrease the prevalence of dental caries in children.