Purpose: is to evaluate the effect of platelet rich fibrin (PRF) on socket healing following extraction of mandibular molars Materials and Methods: This study was conducted as a randomized controlled clinical trial, split mouth design. A total of ten patients, seeking removal of bilateral mandibular molars (20 extraction sockets), were selected to contribute in this study. The selected sample was randomly allocated into two equal groups. Atraumatic extraction of a lower molar has been performed, after an envelope flap was reflected, a PRF membrane was packed over the extraction socket (study site S) where on the control site (C), a collagen membrane was packed to cover the extraction socket of the contralateral side. In both sides, the flap was closed gently by figure of eight sutures. Results: Clinically, swelling values were recorded at 1st, 2nd and 7th days postoperatively, the values of the side S are less than the values of the side C, but these differences were not statistically significant. Pain values were recorded at the first 5 days postoperatively. Less pain sensation in the side S in comparison with side C, but these differences were not significant. The pain in the side S was relieved faster than side C. Conclusions: Within the limitations of this study, it could be concluded that PRF membrane could be used effectively as a socket preservation aid, but it has no effect on hard tissue healing and bone density when compared with collagen membrane. PRF preparation is a technique sensitive, that should be operated carefully, yet it is an easy procedure that have a beneficial clinical and economic effects.