This experimental study aims to evaluate the radiopacity of various fiber post materials and to determine the effects of material composition as analyzed by energy-dispersive X-ray spectrophotometry (EDS; EDAX Team Software; EDAX, Inc., Mahwah, NJ) on radiopacity. Five specimens of seven fiber post materials with 2-mm thickness were prepared and digital radiographs were taken with an aluminum stepwedge (SW) and 2-mm-thick tooth slice. The mean gray values (MGVs) of specimens were measured using the histogram function of a computer graphics program (Adobe Photoshop CS6; Adobe System, Inc., San Jose, CA). The MGVs of fiber post materials were compared with an aluminum SW and dentin of equal thickness. The fiber post specimens were examined by scanning electron microscopy and EDS analysis performed for the elementary analysis of material composition. The MGVs of fiber posts ranged between 83.67 +/- 3.64 and 57.80 +/- 7.08 pixels. Materials were sorted in descending order of MGV as follows: Reforpost, Carbopost, D.T. Light-Post, Easypost, Glassix Radiopaque, Dentolic Glass Fiber Post, and RelyX Fiber Post. All fiber posts demonstrated significantly higher radiopacity values than 2-mm-thick aluminum (p < .05). EDS analysis results indicated that the evaluated fiber posts included various elements for radiopacity in different ratios. All tested fiber post materials showed radiopacity values above the minimum recommendations of the International Organization for Standardization. EDS analysis results indicated that each manufacturer used different compositions of elements like zirconium, barium, titanium, and iron for achieving radiopacity in materials.