Purpose: To evaluate and compare the relative density values of a new endodontic core material (Resilon) and conventional gutta-percha. Methods: 15 Resilon and gutta-percha discs for testing radiopacity were prepared by first coiling three size 35 cones. The coiled material was evenly compressed into the well of a brass mold 10 mm in diameter and a depth of 1 mim. All radiographs were taken on No. 4 ultra-speed dental film. The radiopacity of Resilon, gutta-percha, and dentin slices were then measured with a digital transmission densitometer. Results: The mean radiopacities of Resilon and gutta-percha coiled discs were 4.06 and 7.21 mm of aluminum equivalence respectively, which exceeded the minimal requirement of 3 mm. Both tested materials had lower radiopacity values than dentin. There were highly significant differences in radiopacity values among the tested specimens (P< 0.0 1). Additionally, the mean radiopacity values in root canals were 5.50 and 8.52 mm Al for Resilon and gutta-percha, respectively (P< 0.01). (Am J Dent 2009;22:157-159).