Background: Short and deficiency in the anteroposterior position of the mandible is very common in Class II malocclusion subjects. A small airway dimension during childhood may increase the risk of sleep-related breathing problems during adulthood secondary to fat deposition in the posterior pharyngeal region. The use of functional appliances for the correction of retrognathic mandible is very common in orthodontics. Similar appliances known as oral appliances are also frequently used in adults for the treatment of mild to moderate OSA. Aim of the study: To study effect of treatment with twin block appliances on pharyngeal dimensions in class II malocclusion patients. Materials and methods: The present study was conducted in the Department of Orthodontics and Dentofacial Orthopedics of the dental institution. For the study, we selected 50 subjects 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. The pharyngeal airway passage (PAP) dimension was evaluated from lateral cephalograms. 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 21 and female subjects were 29. We observed that DNP was increased by 0.78, HNP increased by 0.41 mm, DOP increased by 1.95 mm, DHP increased by 1.14 mm, SPL decreased by 0.86 mm, SPT increased by 0.31 mm and SPI decreased by 2.33 mm. Conclusion: Within the limitations of the present study, it can be concluded that twin block appliance can be successfully used for correction of sagittal dimensions of oropharynx and hypopharynx in growing age patients with class II malocclusion. Keywords: Twin block appliance, class II malocclusion, functional appliance.