Objective The purpose of this study was to compare the effects of prednisolone and celecoxib on pain and maximum mouth opening (MMO) after surgical removal of mandibular third molars. Methods and Materials This double-blind clinical study was conducted upon 60 subjects. These patients received 4 tablets of either 100 mg celecocxib or 5 mg prednisolone: one tablet before surgery and the rest for every 8 h postoperation. The subjects were asked to take acetaminophen codeine as rescue dose. Interincisal distance of upper and lower central teeth and pain measurements (according to Visual Analogue Scale) were taken before surgery, 24 h, 48 h and 7 days after surgery. Results Average pain intensity in 24 h after surgery in patients receiving celecoxib was 3.6 ± 2.5 with significant difference to the other group (p = 0.041), but in subsequent evaluations prednisolone group reported less pain intensity, but the differences were not significant. MMO in 48 h after surgery was lower in prednisolone group (p = 0.640) and in further evaluations the groups were almost similar. Analyzing the data revealed no significant difference between groups in MMO. Conclusion According to this study there is no significant difference in the effects of prednisolone or celecoxib upon MMO, while celecoxib had better results for pain relief in 24 h after surgery in comparison to prednisolone.