In the permanent tooth, physiological root resorption does not occur, but inflammatory resorption occurs due to the orthodontic force, ectopic eruption of neighboring tooth and others. In this study, the morphological and histological investigation of the root resorption of the upper permanent incisors caused by the ectopic eruption of the canine was carried out. The left central incisor and lateral incisor from a 12-year-old female were examined. The roots were resorbed almost completely, and in part the resorption extended into the enamel. The results were as follows: 1. In the resorbed dentine, two types of resorption lacuna were observed. One was in direct contact with resorption tissue and the other was repaired with cementum-like tissue. 2. In the resorption lacuna, no odontoclast was recognized. 3. The pulp tissue was normal and the internal resorption was not seen. 4. On the wall of the root canal connected with root resorption, a large amount of hard tissue was formed, and on the external surface of the root, secondary cementum was formed on the primary cementum. 5. Under the scanning electron microscope, the clear dentine tubules in the resorption lacuna, the shallow, unclear resorption lacuna with deposition of the hard tissue and the various steps between them were observed.