Incorporation of fillers into a resin-based material improves some mechanical properties. Objective: The present study aimed to evaluate the effect of filler weight fraction on hardness and flexural strength of a pit and fissure sealant. Materials and Methods: Bis-GMA/TEGDMA-based experimental sealants were prepared by incorporating silanized fillers at 0, 5, 10, 20 and 25% by weight. Microhardness tests (Vickers indenter, 500g, 15s) were carried out on cylindrical sealant specimens (n=5 for each group) using a micro-hardness tester (Future-tech, Japan) after light activation for 20s. Sealant specimens (25x2x2mm, n=7 for each group) were prepared following the same procedure and stored in water (37°C) for 24h prior to the tests. Flexural strengths were measured by the method outlined in ISO 4049 using a universal testing machine (Lloyd, England). Results: There was no significant difference among the flexural strengths of all groups (ANOVA, p>0.05). For hardness, only 25% group (21.47±0.4) showed significantly higher hardness than the control group (18.91±0.3) (ANOVA with Bonferroni test, p<0.05). Conclusion: The addition of fillers at 25% by weight increased hardness of the experimental sealant. This study was supported by National Research Council of Thailand.