Objectives Maxillary transverse deficiency is one of the most common skeletal problems. Patients who have completed skeletal maturity, maxillary transverse deficiency can be treated with surgically assisted rapid maxillary expansion. Orthodontic forces affect the cells in the periodontium to form biologically active substances responsible for remodeling. These substances can be detected in the content of the gingival crevicular fluid (GCF). This study aimed to investigate changes in RANK, RANKL and OPG in the gingival crevicular fluid after surgically assisted rapid maxillary expansion. Materials and Methods A total of 16 patients with a maxillary transverse deficiency were included in the study. Gingival crevicular fluid samples were collected from the mesiobuccal regions of the upper left central, lateral incisors, first and second premolar teeth before the operation (T0), after activation period (T1) and at the 4th month (T2) after the retention period. Changes in RANK, RANKL and OPG levels of gingival crevicular fluid samples were investigated. Results RANK and RANKL amounts were found to be significantly increased in the first and second premolar teeth after expansion, and OPG amounts were significantly decreased in central incisor and first premolar teeth. RANKL was also significantly higher in the first premolar teeth than in the second premolar after retention. Conclusion According to the results of the study, RANK, RANKL and OPG levels are changed in the gingival crevicular fluid after surgically assisted rapid maxillary expansion.