Purpose: To evaluate the clinical performance and marginal microleakage of preventive resin restoration for the treatment of carious lesions in primary and first permanent molars by using three different systems of restorative materials and pits and fissure sealants. Materials and methods: In vivo study: Twenty patients were treated with preventive resin restorations and clinically examined at 3, 6, 9 and 12 months postoperatively. In vitro study: A total of thirty primary and permanent molars were tested for marginal microleakage. Results: There is no statistically significant difference in marginal discoloration, anatomic wear, recurrent caries and surface roughness scores of the three systems in both permanent and primary molars. In marginal adaptation system ӀӀӀ showed the highest rate of success followed by system ӀӀ then system Ӏ . In vitro study: System Ӏ showed the highest dye penetration percentage in both restoration and pits and fissure sealant, followed by system ӀӀӀthensystem ӀӀ. Conclusion: Preventive resin restoration is efficient in controlling dental caries in this critical age (6-9 years).