There is increasing interest in investigating the association between dental caries and childhood obesity, particularly among preschoolers where the evidence is limited. We aimed to measure the prevalence of obesity/overweight among preschool children aged 3 to 6 years, and to determine the relationship between obesity and dental caries in the primary dentition. A cross-sectional study was carried out in eight public and private preschools using a multi-stage stratified sample of 820 children. Waist circumference (WC) and body mass index (BMI) measurements were obtained. Caries was assessed using the National Institute of Dental Research's decayed, missed or filled score (dmft). Based on BMI, 15% of children were obese and 10% were overweight. Based on WC, 13% of children were obese. The prevalence of obesity/overweight based on BMI was significantly higher among girls (p-value=0.014) and private preschools (p-value<0.001). Based on BMI, obese and overweight children had lower dmft scores than underweight and normal children (p-value<0.001). Based on WC, obese children had lower dmft scores than non-obese children (p-value<0.001). Obesity prevalence was high, particularly among girls and private preschool children. Caries activity was lower in overweight and obese children. Longitudinal studies are essential to investigate the association between caries and obesity in preschool children.