Objectives <p>This study aimed to investigate the effectiveness of a national population-based dental sealant in South Korea.</p> Materials and methods <p>This nationwide, population-based cohort study involved all children in South Korea aged 6–7 years who received sealants from 2010 to 2011 and were followed up for 10 years using the Korea National Health Insurance Service (NHIS) database. After 1:2 propensity score matching, 857,723 children were selected for analysis. During the 10-year follow-up, the permanent first molars of the participants were assessed for caries-related treatments (pulpotomy and pulp capping, root canal treatment, and tooth extraction) using multilevel Cox proportional hazards models. The risk of caries-related treatment was lower in the sealant treatment group than in the control group.</p> Results <p>The hazard ratios (HRs) for caries-related treatments among participants were 0.59 (95% confidence interval [CI] 0.57–0.61) for pulpotomy and pulp capping, 0.57 (95% CI 0.55–0.58) for root canal treatment, and 0.29 (95% CI 0.27–0.32) for tooth extraction. This large-scale nationwide cohort study indicated that the sealant treatment in children aged 6–7 years significantly reduced the risk of caries-related treatments (pulpotomy and pulp capping, endodontic treatment, and tooth extraction) by at least 40% during the 10-year follow-up period.</p> Conclusion <p>Sealant treatment in children reduced the caries risk during the 10-year follow-up.</p> Clinical relevance <p>The results demonstrate the effectiveness of the insurance policy for dental sealants.</p>