The purpose of this in vitro study was to evaluate the efficiency of Er:YAG laser on calculus removal and the morphologic changes and hardness of the irradiated surface at different power settings. This experiment used human teeth which were extracted due to periodontal disease and had a band of calculus. Forty root slabs (5x5x2mm3) were made and divided into control group and irradiated groups. Experimental groups were as follows; Control group (root planing), Group 1 (irradiated with laser at 30mJ), Group 2 (irradiated with laser at 60mJ), Group 3 (irradiated with laser at 100mJ). Twelve root slab embedded in resin block were used in each group. Er:YAG laser was applied under water irrigation with the tip held perpendicular to the root surface in contact mode. The treatment time was measured until the calculus was removed completely under naked eyes. The efficiency of calculus removal was evaluated by the time for removal. Morphological changes of laser irradiated site were observed under SEM and the surface hardness was measured using a Vickers Hardness tester. The results were as follows; 1. The efficiency of laser scaling was increased with increasing the energy level of irradiation(p<0.05). 2. The morphological changes such as carbonization, crater and scale-like defects in the irradiated root surface were frequently observed with increasing the energy level. 3. The surface hardness increased at 60mJ and 100mJ irradiated groups than that of control group(p<0.05). From the results evaluting on the efficiency, morphological change and surface hardness, appropriate lower energy level was suggested for the clinical application of the Er:YAG laser in scaling.