Purpose: To evaluate the clinical performance of high viscosity GIC sealant applied with or without additional light curing in children with early childhood caries (ECC). Materials and Methods: A split-mouth clinical trial was conducted in a total of 111 3- to 5-year-old children with ECC. 180 pairs of non-carious primary second molars were selected and divided into two groups: study and control. On the basis of the application technique, selected teeth in the study group were further allotted to group A (sealant application with additional light curing) and group B (sealant application without additional light curing). Caries incidence was observed for 1 year in the anatomical pits and grooves, along with sealant retention and marginal discolouration at various intervals over the 1-year period. Results: Group A (GIC sealant with additional light curing) (44.2%) showed sealant retention similar to that of group B (GIC sealant without additional light curing) (43.0%) (p = 0.885). Caries incidence was significantly higher in the control group (26%) than the sealant groups (1%) (p 0.001). No marginal discolouration adjacent to the sealant was observed in either anatomical grooves or pits in both sealant groups for the duration of the study. Conclusion: Retention and caries prevention by high-viscosity GIC sealant applied with or without additional light curing was found to be similar. At the 12-month assessment, mean dmfs scores and caries incidence in primary second molars were higher in the control than in both study groups. Keywords: ECC, GIC sealants, high viscosity GIC sealant, primary molars