Clinical studies report that failures of fiber post cementation occur mainly at the cement-dentin interface. The aim of this in vitro study is to compare the scanning electron microscopic (SEM) evaluations of the cement thicknesses in the root canals and the thickness of cement-dentin interface zones obtained after luting standardized glass-fiber posts with three different types of luting cements. Thirty single-rooted mandibular premolars of similar sizes were prepared for post insertion after biomechanical preparation and obturation. They were divided into three groups containing 10 samples each. Standardized glass-fiber posts were cemented with zinc phosphate cement for ZNP group, with conventional adhesive resin cement for CAR group, and with self-adhesive resin cement for SAR group. The formation and thickness of cement and cement-dentin interface zone were evaluated by stereomicroscope and SEM using x800 magnification, and the data were analyzed. There was no significant difference between groups in terms of cement thickness (p=0.835); however, there were significant differences among the cement layer thicknesses measured at the three examined levels of the root canals (p=0.000). The groups using conventional adhesive resin cement presented longer micromechanical interlocking while the groups using self-adhesive resin cement showed wide gaps and zinc phosphate cement showed no bonding between cement-dentin interdiffusion zones along the root canal. As a clinical consequence, the use of zinc phosphate cement may not provide strong bond between dentin-cement interface. Conventional adhesive resin cements showed reliable bond to dentin when compared to zinc phosphate and self-adhesive resin cement.