This study aims to investigate the effectiveness of a nutritional counseling program for mothers of newborns to prevent sugar consumption in the first year of the child's life on the occurrence of Early Childhood Caries (ECC). A multicentric randomized clinical trial (ClinicalTrials.gov NCT03841123) was conducted in three state capitals of Brazil (n=516). Mothers were randomly assigned to the intervention group (IG) or control group (CG) after delivery. The IG received face-to-face nutritional counseling based on UNICEF dietary guidelines, followed by monthly phone calls. The CG received standard counseling. Dietary intake was measured through structured questionnaires and 24-hour recalls at six and 12 months. Calibrated dentists performed a dental clinical examination for ECC diagnosis after the children completed their first year of life. The prevalence of ECC was 17.4% in the overall sample (49/290). The number of affected teeth ranged from 0 to 6 (mean 0.43). The IG had a 2.4 times probability of not consuming sugar in the first six months of the child's life (RR 2.44; 95% CI 1.18-5.00) and they had Fa significantly lower mean number of sweet items consumed at 12 months (p=0.016). No significant differences between groups were found concerning the occurrence of ECC (RR 1.33; 95% CI 0.79-2.25) or the number of teeth affected by caries (p=0.273). The intervention to prevent and reduce sugar intake in the first year of life was not effective at reducing the occurrence of early childhood caries or the number of teeth with carious lesions.