Objective: To evaluate the retention and caries preventive effect of a recently developed local sealant compared with an imported material on lower first permanent molars at 18 months. Methods: The study group comprised 145 pairs of contralateral lower first permanent molars in 6-9 year old children from Saraburi province, Thailand. A matched pair experimental design was used in which the local sealant (Prevocare, Thailand) and Concise (3M Dental Products, U.S.A.) were randomly allocated to one of the teeth within each pair. Results: After 18 months, 132 pairs (91%) of molars were examined by a different evaluator. Complete retention rate in the experimental group (Prevocare) was 93.2% with the 95% CI of 88.8 to 97.5% while the retention rate of the conventional group (Concise) was 93.9% (95% CI 89.8, 98.1%). The mean difference in retention rates between the two groups was -0.7% (95% CI – 6.4, 4.9%). None of the sealant was completely loss and no carious lesions developed in the sealed teeth during the trial. Conclusion: Prevocare was clinically equivalent to Concise, in terms of retention and caries prevention on first permanent molars at the period of 18 months. This study was supported by the Faculty of Dentistry Research Fund.