Objective: The effectiveness of seals obtained after cementation of fiber posts into root canals is still unclear. The aim of this in vitro study was to evaluate the influence of ethanol treatment on the bond between root canal surfaces and fiber posts. Method and Materials: Forty sound extracted teeth were selected for this study. The specimens were endodontically treated, and a post space was prepared. In half of the teeth, the post space was etched and bonded (group 1); in the other half, it was etched, dried with ethanol, and bonded with the same adhesive system (group 2). A fiber post was placed in each root using the same adhesive and restorative protocol. Restored samples were perpendicularly sectioned at the coronal, middle, and apical third and prepared for SEM observation to evaluate the interfaces among root dentin, resin cement, and fiber posts, as well as the characteristics of the resulting hybrid layer. Results: SEM examination of interfaces among root dentin, resin cement, and fiber posts showed differences in adhesive interfaces between the groups. No significant differences (P > .05) were found at the cement-post interface. At the dentin-cement interface, group 1 showed significantly lower scores (P .05) than group 2. In both groups, the cementpost interface showed significantly (P .05) lower gap scores than the dentin-cement interface. Conclusion: Ethanol drying does not seem to be effective in improving the adhesion of fiber posts into root canals. Keywords: adhesive interfaces, ethanol, fiber post, resin cement, resin-dentin interdiffusion zone, scanning electron microscopy