PURPOSE: The purpose of this study is to compare three different CAD/CAM systems through the fracture strength of zirconia core and to evaluate the clinical availability of each system. MATERIAL AND METHODS: The following three groups of 30 maxillary mesial incisor core for all-ceramics(each group 10) were fabricated as follows: group 1. Adens(R) CAD/CAM system, group 2. Cerasys(R) CAD/CAM system, group 3. 3M LAVA(R)CAD/CAM system. All specimens were manufactured consistently thickness 0.5mm and relief 40 micrometer. Specimens were subjected to compressive loading on the lingual area by Z250/SN5S(R). Each group's mean and standard deviation were calculated and Kruskal Waillis test, Wilcoxon Rank Sum test were utilized to find out the relationship among the groups. RESULTS: The results were as follows: 1. The mean fracture strength of Adens(R) system was 615.89+/-156.1N, the Cerasys(R) system was 863.98+/-151.5N, and the 3M LAVA(R) system was 1143.1+/-286.6N. 2. The fracture strength of the systems showed the significant statistical differences in order of 3M LAVA(R) system, Cerasys(R) system, Adens(R) system. CONCLUSION: In this study, in spite of the differences among the groups, every group showed clinically useful results. It is necessary to study further clinical experiments on a long term basis.