Objective: To explore the effect of miniscrew-assisted rapid palatal expansion (MARPE) on mandible position in the treatment of adult skeletal Class Ⅰ malocclusion with maxillary transverse deficiency. Methods: In this retrospective study, 20 cases of adult skeletal Class Ⅰ malocclusion with maxillary transverse deficiency treated with MARPE in our hospital from July 2019 to March 2022 were selected as research objects. CBCT data of three time points before treatment (T0), immediately after expansion (T1) and six months after retention (T2) were collected. The head position was standardized and calibrated by Dolphin software, and then mandible landmarks (left and right Condylion, left and right Gonion, Menton) were positioned. The linear distance changes of each landmark relative to the reference plane of coronal plane, axial plane and sagittal plane were measured, which represented the sagittal, vertical and horizontal displacement of mandible respectively. Repeated measurement ANOVA and LSD multiple comparison were used to evaluate the position change of each landmark. Results : The Menton and right Gonion rotated clockwise at T1, and relapsed to the initial position at T2. No lateral displacement of Menton was found. Conclusion When MARPE is used to treat skeletal Class Ⅰ malocclusion with maxillary transverse deficiency, it causes a transient clockwise rotation of the mandiblar. The mandible does not show sagittal, vertical and horizontal position changes in long-term evaluation.