The feasibility of quantitatively evaluating the surface character of dentin after Er:YAG laser irradiation by using optical coherence tomography (OCT) is examined. Dentin specimens were prepared from human extracted third molars free of decay. Er:YAG laser non-contact irradiation was performed at pulse duration of 50?μs under water spray. The control groups were sandpaper polishing group and traditional bur treated group. OCT techniques were used to observe the surface properties and measure the changes of surface light intensity of dentin specimens. Histopathological sections were used to analyze the surface structure. Then 37% phosphoric acid was etched for 30 seconds after surface treatment, and the surface morphology was then observed by scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy was used to measure the composition of surface elements. OCT results demonstrated that a layer with high image intensity generated on all experimental dentin surface. Quantitative results obtained that the thickness of these affected layers produced by Er:YAG laser was markedly higher than those of bur- and sandpaper-treated groups (P<0.05). Histology demonstrated that thin denatured layers were created in laser-treated dentin. Little denatured layer on bur- and sandpaper-treated area. The modified layer of histological examination was consistent with the light intensity changes of OCT images. After acid treatment, the dentinal tubules’ entrance enlarged, whereas collagen fibrils network was not exposed in the SEM images of Er:YAG laser groups. After acid treatment for the same time period, EDX spectroscopy showed that the content of Ca and P ion in laser-treated group were higher than bur- and sandpaper-treated groups (P<0.05), which means the laser-treated dentin becomes being more acid resistant. This study demonstrated OCT may become a noninvasive tool to precisely evaluate the character of dentin that would be useful to dentists in helping determine adhesive restoration strategies.