Purpose: To evaluate the changes in upper airway volume and sleep parameters in edentulous class II OSA (Obstructive Sleep Apnea) patients treated with mandibular advancement splint (MAS) fabricated at different jaw positions. Materials and Methods: Thirty five patients were selected based on inclusion ans exclusion criteria and were randomly divided into two groups i.e. Group I and Group II. For patients in Group I, mandibular advancement splint (MAS) was fabricated at 60 % of mandibular protrusion and for patients in Group II, MAS was fabricated at 70 % of mandibular protrusion. Four variables were assessed at baseline and 6 months after wearing MAS. These variables were: AHI, oxygen desaturation events/hr, mean O2 saturation and total upper pharyngeal volume. Results: All the subjects showed an increase in pharyngeal volume at both level of mandibular advancement. There was a drastic improvement in AHI values from 21.76 to 15.82 at 60 % of mandibular advancement and 17.76 at 70 % of mandibular advancement. On evaluating the percentage change in pharyngeal volume at various levels of mandibular advancement using regression analysis, the following equation was derived: Percentage change in volume (Y) = 0.347*X +57.55. Where percentage change in volume is dependent (Y) and percentage of mandibular advancement (X) is independent. Conclusion: Present studied showed that mandibular advancement splint is effective in increasing the upper airway volume and reducing the severity of OSA. Also the percentage change in posterior pharyngeal volume is directly proportional to mandibular advancement up to certain limit.