Objectives: The purpose of this study was to evaluate the microleakage along RelyX Fiber post cemented with five different materials: RelyX Unicem, Calibra, Multilink, zinc-phosphate Harvard cement and AH Plus using a dye penetration and dye extraction method. Materials and Methods: Seventy-five extracted single-rooted human teeth were prepared and obturated with cold lateral condensation of gutta-percha and AH Plus. The coronal third of the filled canals were prepared using a special reamer for RelyX fiber post (3M ESPE, Seefeld, Germany) to a depth of 12 mm.The samples were randomly divided into five experimental groups with 15 specimens each and RelyX fiber post were cemented with RelyX Unicem (3M ESPE, Seefeld, Germany), Calibra (DeTrey, Dentsply , Konstanz, Germany), Multilink (Ivoclar Vivadent, Schaan, Liechtenstein), AH Plus (DeTrey, Dentsply, Konstanz, Germany) and zinc-phosphate Harvard cement (Richter & Hoffmann, Germany) according to the manufacturers` instructions. The coronal leakage was evaluated with dye penetration method using a centrifuge for three minuts at 30 g in 2 % methylene blue. After then the teeth were rinsed under water and dissolved in 65 % nitric acid for 3 days to extract methylene blue. The absorbance was determined with a Biophotometer (Eppendorf Biophotometer, Germany). Statistical analysis was performed using the Kruskal-Wallis-H-test and the Mann-Whitney-U-test. Results: Statistical analysis showed significant difference in leakage between the group RelyX fiber post / zinc-phosphate Harvard cement and all other groups luted with RelyX Unicem, Multilink Calibra and AH Plus (p < 0.05). No statistically significant difference was found between the RelyX Unicem, Calibra, Multilink and AH Plus groups. Conclusion: This in vitro study found that RelyX fiber post luted with RelyX Unicem, Calibra, Multilinik and AH Plus showed less dye penetration than RelyX fiber post cemented with zinc-phosphate Harvard cement.