Objective: Microleakage evaluation of a composite core build up material (Build-It!-FR, Jeneric/Pentron Inc. Wallingford, CT, (J/P)) with and without an unfilled resin (Protect-It!, J/P). Method: 120 extracted human molars were accessed endodontically. Dowel space was created . The teeth were randomly divided into four groups of thirty. Dowel spaces and cut surfaces were etched (37% phosphoric acid, J/P) and bonding agent (Bond1, J/P) applied according to manufacturer’s instructions. A 1.25mm Fibrekor dowel (J/P) was inserted and cemented (Cement-It!, J/P). Group 1 served as control and all teeth restored only with Build-It!(J/P). After setting of the material, excess was removed to simulate crown preparation. Group 2 received Build-It! and Protect-It!. Group 3 had flowable composite (Flow-It!, J/P) and Build-It!. Group 4 was treated the same as Group 3 and had Protect-It!. Specimen were placed in 37C and 100% humidor. Ten teeth from each group were removed at 1, 4, 6 weeks. Teeth surfaces were covered with nail varnish 1 mm from the preparation, and soaked in 2% methylene blue for 24 hours at room temperature. Specimens were sectioned horizontally and vertically. Specimens were viewed and leakage results recorded. Results: No microleakage was found between the post and the Cement-it!. One way ANOVA and POST HOC tests showed 95% confidence interval for occlusal leakage was between 0.26 and 0.43 and gingival leakage was between 0.73 and 0.87. The F value for occlusal leakage was 18.6 (p<0.001) and gingival leakage was 14.8 (p<0.001). Conclusion: Application of unfilled resin on prepared direct dowel and core preparations decreased leakage but did not prevent it. Leakage occurred as early as one week.