This study was aimed to demonstrate whether laser treatment on dentin is effective to improve the marginal and internal fit of CAD/CAM occlusal veneers, which is a conservative restoration for severe tooth defect from abrasion. Sixteen extracted molars were divided into 4 groups according to adopting laser treatment on dentin and milling materials (n=4): Lava Ultimate CAD/CAM Restorative with no laser treatment on dentin (group LU-C), Lava Ultimate CAD/CAM Restorative with laser treatment on dentin(group LU-L), IPS Empress CAD with no laser treatment on dentin(group IE-C) and IPS Empress CAD with laser treatment on dentin(group IE-L). After the restoration adhesion, all of specimens were scanned by micro-computed tomography(micro CT) to evaluate the marginal and internal fit of each specimen by artificial setting measuring points from both bucco-palatal and mesio-distal direction. For marginal fit, there was no statistical difference with or without laser treatment on dentin for either milling material. For internal fit, the situation was identical. Laser treatment on dentin would not affect the marginal or internal fit of CAD/CAM occlusal veneers, therefore, it may not be necessary for improving the fit of restorations.