Objective:To observe effects of Gelatamp colloidal silver gelatin sponge in preventing complications caused by extraction of impacted mandibular third molar. Methods: Total 582 patients with impacted mandibular third molars were quasi-randomly assigned into two groups with 297 in the test group and 285 in the control group. In test group,Gelatamp colloidal silver gelatin sponge was put into the socket after the extraction of impacted mandibular third molar,while nothing was put into the socket after the extraction in control group. Patients visited at 0.5 h,3 d and 7 d after the extraction. Complications were observed and the incidence rate was calculated. Results: The incidence rate of postoperative complications in test group was lower than that in control group,and there were significant differences between the test group and the control group(P < 0.05) Conclusion: Gelatamp colloidal silver gelatin sponge can effectively prevent complications caused by extraction of impacted mandibular third molar. Therefore it is recommendable in clinical practice.