A micro morphological study was performed; this study compared the interface between radicular dentin and resin cement, when fixing fiberglass posts with Relyx Unicem™ and ParaCem™ systems. Twenty single-rooted premolars, extracted by orthodontic indication, were divided randomly into two groups of 10 teeth each. Endodontic treatment using gutta-percha points and Grossman cement was performed. The samples were partially desobturated and the fiberglass posts (Tenax Fiber White, Coltene Whaledent) were fixed with the resin cements. The teeth roots were cut at one third, apical-center and cervical and prepared for a SEM observation. The posts cemented with Relyx-Unicem™ didn't show a hybrid layer formation on any of the root thirds. The cement-dentin interface was found irregular and discontinuous. However, a very close union between post and cement was found. The roots on which ParaCem were used formed a uniform and homogeneous hybrid layer with a thickness average of 2 μm only on the cervical third, not on the center and apical thirds. A close post-cement union was detected, except on the apical third. No formation of tags on this study was observed.