To investigate effect of platelet-rich plasma(PRP) on proliferation and differentiation of postnatal stem cells derived from human dental tissues, we isolated stem cells from dental tissues such as dental pulp, periodontal ligament, and surrounding mandibular bone. The isolated dental stem cells were tested on colony forming ability, proliferation, and ALP activity at different concentration of PRP. All of dental stem cells showed high proliferation as increased concentration of PRP. On the contrary, high concentration PRP such as 5% inhibited proliferation of stem cells. These results suggest that the proper concentration of PRP can be utilized to accelerate the proliferation of human dental stem cells.