Objective:To investigate the in vitro effects of platelet-rich plasma(PRP) on human periodontal ligament fibroblasts(PDLFs). Methods: Various concentrations of PRP (10, 50, 100, 200, 300, 500 ml/L) were applied to primary cultures of human PDLFs. MTT assays were utilized to assess cell proliferation ability. Migration was determined by assessing the cell response to a concentration gradient with Transwell chamber. Differentiation was assessed using alkaline phosphatase (ALP) kit. Results: A beneficial effect on proliferation was observed, especially in response to 200 ml/L PRP.PRP had stimulatory effects on the migration of human PDLFs. PRP facilitated differentiation of PDLFs. Conclusion: PRP can exert a positive effect on human PDLFs,but this effect is concentration specific, while higher concentrations is not necessary to result in optimal outcomes.