Dental laser provides many advantages to the clinicians. Those are excellent hemostatic effect, good operating sight, minimal adjacent tissue injury, reduction of postoperative swelling & pain, reduction of postoperative infection, reduction of scar tissue & contraction, etc. The purpose of this study is to observe how these advantages work after surgical extraction of impacted third molar. From march 2000 to july 2000, we have randomly divided the patients who had been surgically extracted unilateral impacted third molar into two groups. The first group comprised $CO_2$ laser illumination with 3 watts, defocusing & continuous mode, rotating motion for about 3 minutes after finishing of surgical extraction & suture. The other group patients were not irradiated. The medications in two groups were same. We measured pain, swelling and trismus three times(pre-operation, first day after operation, and 7th day after operation). The number of the patients who had measured three times all are 64, laser irradiated groups are 36 and non-irradiated groups are 28. The age ranged from 19 to 50, with a mean of 27.9 years. The operative time ranged from 3 minutes to 50 minutes, with a mean of 12.1 minutes. In the $CO_2$ laser group, the pain intensity of the 7th day after operation was still increased significantly comparing with that of the pre-operation and the distance which were measured for the swelling was different significantly. In the other group, the mouth opening limitation was still decreased significantly.