A rare case-a 11-year-old boy with ectopic eruption of all the permanent second molars associated with resorption of all the permanent first molars was reported. Severe root resorption was found in the mandibular first molars, while moderate root resorption was found in the maxillary first molars. There were several points should be addressed into consideration: (1) young age; (2) the third molars will probably be brought into occlusion in the future; (3) Class III jaw relationship. The orthodontic treatment was approached with twostage. Stage I treatment was aimed to upright the mandibular second molars after removal of the mandibular first molars. Full mouth comprehensive treatment will be performed in stage II after serial follow-up and reevaluation. Two-stage treatment in such a case will thus reduce the uncertainty of facial growth related malocclusion and unexpected treatment duration.