INTRODUCTION: Avulsion of teeth radically affects the integrity of the tooth and the supporting tissue, and impairs the natural dentition as a whole; thus, all efforts must be directed to the replantation of traumatically avulsed teeth. However, its success is limited due to the occurrence of external root resorption. The challenge is to follow an effective protocol that reduces the occurrence of root resorption and allow for reestablishment of the natural architecture of the periodontal tissue. Biomodulation provided by low level laser therapy provides a promising tool in managing the inflammatory process and augmentation of the reparative process. OBJECTIVES: Was to evaluate the effect of low-level laser therapy (LLLT) on the healing process of rat teeth replanted after delayed replantation. MATERIALS AND METHODS: Thirty healthy Albino male rats had their maxillary left incisors extracted; According to the root surface treatment before the replantation, the teeth were assigned randomly to two groups (n = 15): G1 (control)-no root surface treatment; G2 (study group)-laser diode treatment on the root surface. The teeth were replanted into their respective sockets after 30 minutes, mimicking the natural timing it would take to replant an avulsed tooth. G2 were treated with LLLT performed on the buccal and palatal mucosa every 48 hours for 15 days. The rats were sacrificed after 15, 30 and 45 days of replantation. The specimens were processed for histological and histomorphometric analysis to determine the average root resorption areas and to evaluate the histological events. RESULTS: Histomorphometric analysis showed that the study group (Laser irradiated group) showed lower areas of root resorption and ankylosis, than in control group (non-irradiated group); with a significant statistical difference (p > 0.05). Histological assessment showed restoration of periodontal ligament attachment and increased vascularity in the study group. CONCLUSIONS: Laser irradiation reduces external root resorption and ankylosis in delayed tooth replantation.