Background: Pain, swelling and trismus are the main minor complications encountered after surgical extraction of impacted third molars, minimizing these postoperative complications is the center of many studies, one proposed method is the prophylactic administration of corticosteroids, the aim of this study is to evaluate the effect of prophylactic Dexamethasone administration on facial swelling and trismus after surgical extraction of impacted third molars. Materials and methods: 20 patients were included in this study, they were randomly divided into 2 groups of 10 patients each; a study group in which patients were given 8 mg. Dexamethasone 1 hour before surgical extraction of impacted third molar and 4 mg. 6 hours postoperatively, and a control group in which no drug was given, mouth opening and direct facial measurements were done preoperatively and 2 days postoperatively, data were collected and analyzed. Results: The study group showed less facial swelling and trismus postoperatively, in facial swelling the difference was statistically significant, while for trismus the difference was not significant. Conclusion: Prophylactic administration of Dexamethasone reduces facial swelling and trismus after surgical extraction of impacted third molars.