The purpose of this study was to observe and measure the morphological changes that occur in the hard tissue after the application of Er: YAG laser. Another objective was to evaluate and compare the duration of application of both the laser apparatus and a conventional cutting device. In this study, sound and newly extracted carious tissues were used. The morphological changes in hard tooth structures produced by Er: YAG laser irradiation were examined by using a laser scanning microscope. Results showed that appropriate laser irradiation was 100 mJ/pulse for dentin, and 200mJ/pulse for enamel. Also, the laser scanning microscope images were less damaged than the SEM images due to pretreatment of the specimens. The time taken to remove carious enamel by laser irradiation was slightly longer than the compared rotary cutting device; however, no differences between the two methods were observed in case of carious dentin removal.