Background: To assist the retention of restorations prepared in endodontically treated teeth, fiber posts are widely used in dental practice. The ideal time to prepare space for the post is still controversial. Aim: The purpose of this study was to evaluate the effects of immediate and delayed postspace preparation on the retention of the self-adhesive resin cement. Materials and Methods: Twelve bovine teeth were used with sectioned roots standardized to 19 mm. The teeth were properly instrumented and filled with gutta-percha and eugenol-free cement AH Plus. Two experimental groups (n = 6) were created based on the different times of post preparation (immediate and delayed). Using cemented cylindrical fiber posts, the teeth were put in acrylic resin and polyvinyl chloride tubes, where the cuts were made. Two slices were obtained from the cervical third, two from the medium third and two from the apical third. Subsequently, the samples were subjected into push-out tests. Statistical analysis were performed using ANOVA and Tukey's test (P = 5%). Results: The results indicated that, for all of the evaluated thirds, delayed preparation showed greater bond strength than immediate preparation. Conclusion: A delayed post preparation of the root space, following the root canal filling, is recommended.