PRP is used in various fields of medicine, such as dentistry, orthopedics, and plastic surgery, to promote early tissue healing and regeneration, and has recently received recognition because of its increased use in injured athletes. Platelets are important cells that initiate wound healing. PRP is a normal autologous component of blood that contains many platelets. There are three types of granules in platelets. The α granules are storage granules containing various growth factors, such as PDGF, VEGF and CTGF. Growth factors released from platelets become active through the coagulation process, and their release upon the destruction of α granules stimulates tissue regeneration. Previous studies have reported that PRP significantly induces the proliferation of various cells, such as human adipose-derived stem cells, human dermal fibroblasts, periodontal ligament cells, and alveolar bone cells. A recent study reported that PRP injection into the knee joint promoted cartilage healing. However, there are few studies dealing with synovial cells, and the effect of PRP on proliferation of human synovial cells is uncertain. We investigated the influence of PRP on human synovial cells to clarify the clinical efficacy of PRP for synovial membrane tissue injury associated with temporomandibular joint disorder and related diseases in the field of oral surgery.