Introduction: This study aimed, effect of PLATELET-RICH PLASMA (PRP) on soft tissue healing after mandibular third molar surgery. Materials & Methods: In this semi-blinded clinical trial study, 30 selected patients requiring surgical extraction of soft tissue impacted mandibular third molar participated from cases referred to the Department of Surgery, Faculty of Dentistry, Isfahan Azad University 2017. Patients divided into both test and control groups. PRP was placed in the extracted socket of the test group, whereas the control group had no PRP. Arzhangian standard kit utilized for preparation of PRP. The outcome variables in this study were pain, swelling, inter incisal mouth opening, wound dehiscence, dry socket, bleeding, and tissue color. The collected data analyzed using statistical tests followed independent T-test, Mann-Whitney, and fisher (p value < 0. 05). Results: The mean postoperative pain score (Visual Analog Scale) lowered for the test group after several wound dehiscence on the third and seventh days after surgery which was statistically significant (p value < 0. 001). Although the mean bleeding time on the third day after surgery decreased in the test group, this difference was not statistically significant (p value = 0. 59). There were no statistically significant between both groups for The dry socket incidence on the seventh day and the mean of inter incisal mouth opening in the third and seventh days after surgery as well. Conclusion: The usage of topical PRP has beneficial advantages on soft tissue healing after mandibular third molar surgery. Unlike the control group, The PRP group provided reduced pain and better soft tissue healing.