Objectives : The purpose of this study is to evaluate effectiveness of ROK dental CAD/CAM(computer-aid design/computer-aid manufacture) system, which is newly introduced since 2015 by measuring marginal fitness of all ceramic final prostheses(zirconia crown) in labial(buccal), palatal(lingual), mesial and distal marginal area on molar and premolar teeth. Methods : twenty patients who need caries removal and prosthetic treatment participated in this study to fabricate crown prostheses by using ROK dental CAD/CAM system. total twenty-four teeth(seven maxillary premolar, six maxillary and mandibular molar, five mandibular premolar) are treated to CAD/CAM prostheses. final prostheses is adapted to teeth, and marginal fitness was evaluated by using replica technique. Results : labial/buccal marginal gap of bucco-lingual section is 57.1μm(±11.8μm), palatap/lingual is 64.9μm(±17.3μm), and mesial marginal gap of mesio-distal section is 61.9μm(±9.6μm), distal area is 62.5μm(±13.8μm). In comparison of tooth area, the marginal gap of maxillary premolar, mandibular premolar, maxillary molar, mandibular molar is respectively 54.9μm, 63.9μm, 64.0μm, 64.8μm. In periodic check after 1 month, non specific finding is seen such as periodontal or prosthetic problem. Conclusions : In this study, mean marginal distance of zirconia crown prostheses by using ROK dental CAD/CAM system is 61.6μm, so it seems that it had clinically acceptable marginal fitness.