Objective – To test the hypothesis that immunosuppressant tacrolimus treatment can interfere with bone turnover and rate of tooth movement. Material and Methods – One-hundred twenty Wistar male rats were divided into four groups: Group 1 (rats subjected to orthodontic movement plus treatment with saline solution vehicle), Group 2 (rats subjected to orthodontic movement plus treatment with FK506), Group 3 (rats treated with FK506 only), and Group 4 (rats treated with saline solution vehicle). The maxillary incisors were laterally moved with a reciprocal load of 35 cN. The dosage of FK506 was 2 mg⁄ kg ⁄ day. Howship s lacunae, osteoclasts, and macrophages were counted. Results – Tooth movement was found to be greater in Group 1 than in Group 2 for all time periods (on days 3, 7, and 14), although a significant difference was observed only on days 7 and 14 (p < 0.05). The number of osteoclasts was smaller in Group 1 than in Group 2, whereas the number of Howship s lacunae was greater. Conclusion – FK506 has the capacity of promoting osteoclasts inhibition with probable osteoclastic apoptosis of alveolar bone following tooth movement.2030-01-01