Abstract: Objective: To evaluate changes and correlations of masticatory muscles in class II division 1 malocclusion adult patients after orthodontic treatment by cone beam computed tomography (CBCT). Methods: In total, 60 patients with severe class I (n=30) or class II division 1 (n=30) malocclusion were enrolled. Morphological parameters of CBCT (including ascending mandibular ramus, masseter muscle, medial pterygoid, and lateral pterygoid) of these patients before and after the orthodontic treatment were collected. The changes before and after treatment regarding these parameters were compared. Results: There were significant differences in the width, angle of masseter muscles of class I, and the width, angle, thickness of masseter muscles of class II division 1 (P< 0.05). There were significant differences in the width, thickness, area of medial pterygoid muscles of class I (P< 0.05). There were significant differences in the area of lateral pterygoid muscle in upper level of class I and the thickness, area of lateral pterygoid muscle in upper level of class II division 1 (P< 0.05). Conclusions: There were differences morphological changes of masseter, medial pterygoid, and lateral pterygoid muscles between class I and class II division 1 patients.