Background: Class II division 1 anomalies result from mandibular inadequacy rather than from excess of maxillary development. Considering its effects on airway dimensions, correction of class II malocclusions is not only important in terms of aesthetics and function, but also in terms of increasing patient comfort. Studies have shown that if the skeletal Class II malocclusion is diagnosed at an early age, the best treatment option is the use of functional appliances, which allows the forward growth of the mandible and prevents upper airway collapse during sleep. Aim of the study: To study the effect on pharyngeal dimensions of class II malocclusion patients with Twin block appliance. Materials and methods: The present study was conducted in the Department of Orthodontics and Dento-facial orthopedics of the Dental institution. For the study, we selected 50 patients in the age range of 8 to 14 years with skeletal class II malocclusion associated with mandibular retrusion. The class II malocclusion in treatment group subjects was corrected by standard twin-block appliance. One-step mandibular advancement was carried out during the wax bite registration. An edge-to-edge incisor relationship with 2- to 3-mm opening between the maxillary and mandibular central incisors was maintained for all subjects. Results: A total of 50 subjects were included in the study. The age of subjects ranged from 8-14 years. Number of male subjects was 24 and female subjects were 26. DNP was increased by 1.28 mm, HNP increased by 2.3 mm, DOP increased by 2.69 mm, DHP increased by 2.2 mm, SPL decreased by 2.11 mm, SPT increased by 0.86 mm and SPI decreased by 7.25 mm. Conclusion: Within the limitations of the present study, it can be concluded that treatment of class II malocclusion patients with twin block appliance leads to correction of sagittal dimension of oropharynx and hypopharynx. Keywords: Twin block appliance, class II malocclusion, orthodontic treatment, functional appliance