STATEMENT OF PROBLEM: There have been many studies about marginal adaptation of Zirconia core fabricated with various CAD/CAM systems. But, the comparative study has not been conducted much. PURPOSE: This study was to compare marginal adaptations of zirconia cores fabricated with 3 different CAD/CAM systems. MATERIAL AND METHODS: The in vitro marginal adaptations of zirconia cores fabricated with 3 different CAD/CAM systems(Adens(R) system, Lava(R) system, and Cerasys(R) system) were evaluated and compared. In this study 30 zirconia cores were fabricated(10 zirconia cores per each system). The measurements of the marginal adaptatioin were carried out using microscope L-150A(R)(Nikon, Japan). Measurements were recorded at 50 points. The measurements were analyzed using Kruskal-Wallis test and Wilcoxon rank sum test. RESULTS: Within the limits of this study, the results were as follows. 1. Mean marginal gap values obtained were 284.5+/-152.9 micrometer in Adens(R) system, 99.0+/-73.0 micrometer in Lava(R) system, and 153.5+/-85.7 micrometer in Cerasys(R) system. 2. Zirconia core made by Lava(R) system showed the smallest marginal gap(P<0.05). CONCLUSION: In the limitation of this study, we concluded that Lava(R) System was superior than other systems(Adens(R) system and Cerasys(R) system) in the marginal adaptation.