The purpose of this study was to examine histologically and radiographically the effect of a bleaching agent, a mixture of sodium perborate and superoxol (30% hydrogen peroxide), without a heat source on the cervical root surface and periodontal tissue of endodontically treated teeth of dogs. Endodontic treatment was performed on anterior teeth of dogs. The endodontically treated teeth were then divided into two groups. One group received walking bleach procedures, while the other group did not. The animals were killed at intervals of 1 and 3 months after bleaching for histological and radiographic examination. External cervical root resorption was only observed in bleached teeth at 3-month but not at 1-month observation.