Purpose: The surgical extraction of lower third molars is the most frequent intervention in oral surgery. Swelling, trismus and pain are normal phenomena induced after surgical removal of impacted mandibular third molar. The use of corticosteroids has gained wide acceptance to reduce postoperative complications. Many studies have used dexamethsone in dentoalveolar surgery to reduce facial swelling, pain and trismus but the comparative study on half an hour preoperative intramuscular and intravenous injection of dexamethasone has not been undertaken for studying its effect on postoperative sequlae of surgical removal of mandibular third molar which has been done in the present study. Methodology: Study was conducted on 15 patients with bilaterally impacted mandibular third molars with similar difficulty index. The patients were given single preoperative dose of 8mg intravenous and intramuscular dexamethasone for surgical removal of impacted mandibular third molar with a minimum interval of 1 month between two surgeries. Pre operative and first, third and seventh postoperative day’s inter-incisal distance, facial swelling & pain was assessed based on VAS. The data was subjected for statistical analysis. Results: The significant lower values of pain score on VAS scale were noted with the intravenous route of administration of dexamethasone. Conclusion: This study reveals that the half an hour preoperative intravenous route of administration of dexamethasone is preferable over the intramuscular route to reduce the incidence of post operative pain on surgical removal of impacted mandibular third molar.