The present study reports a case of intentional replantation (IR) for a right mandibular second premolar (#45). For the present case, root canal retreatment was first considered after removal of the metal post and core. When the metal post and core could not be removed from #45, micro-apical surgery or intentional tooth replantation was performed. Six-month postoperative evaluation revealed that the right mandibular second premolar had no obvious symptoms of discomfort, and the clinical follow-up revealed uneventful healing and good bone regeneration. The short-term clinical efficacy was acceptable. For cases with root canal treatment failure, when the apical surgical access could not be established due to the adjacent important anatomical structures, IR may be employed as an accepted endodontic treatment procedure. Key Words: Root canal treatment failure, Post-core crown, Root canal retreatment, Intentional replantation.