Background: Postoperative pain is one of the main complications following impacted mandibular third molar (IMTM) surgery. Objectives: The aim of this study was to assess the effect of the local application of bupivacaine on reducing early postoperative pain following IMTM surgery. Material and methods: A prospective, single-blinded, randomized controlled study was conducted on 40 patients who had undergone the surgical removal of an IMTM under local anesthesia. In the study group (n = 20), absorbable gelatin sponge (AGS) soaked in 3 mL of 0.5% plain bupivacaine hydrochloride was locally applied in the post-extraction socket. In the control group (n = 20), AGS soaked in 3 mL of normal saline was used. Pain intensity was assessed using a pain numerical rating scale (NRS) 4 and 12 h postoperatively. The variables were compared between the 2 groups and probability values <0.05 were considered statistically significant. Results: The pain scores in the study group were significantly lower than those recorded in the control group at 4 h postoperatively (p = 0.003), whereas the difference in the pain scores between the 2 groups 12 h after surgery was not statistically significant (p = 0.443). Conclusions: The local application of bupivacaine is effective in reducing postoperative pain 4 h after the surgical extraction of IMTMs without any significant complications.