Abstract: Objective To evaluate the effect of aging on the proliferative and differentiation capacity of human periodontal ligament stem cells (PDLSCs). Methods Human periodontal ligament tissues were obtained from surgically extracted third molars from 6 subjects aged 18-20 years (group A) and 6 subjects aged 45-50 years (group B). The proliferative capacity of PDLSCs isolated from the tissues was examined with MTT assay, and the osteogenic and adipogenic differentiation capacity of the cells were evaluated using alizarin red staining and oil red O staining. SA-βG expression was analyzed to assess the cell senescence. In both groups, PDLSCs were induced for osteogenic differentiation for 7 days, and the differentiation ability of the cells was assessed by examining alkaline phosphatase (ALP) activity and by detecting the expressions of osteocalcin (OCN) and ALP using Western blotting. Results Human PDLSCs were successfully isolated from the 12 teeth and were characterized as MSCs. The PDLSCs derived from donors of different ages were all capable of osteogenic and adipogenic differentiation, but their proliferative and osteogenic differentiation capacity decreased with the donors’ age. The cells also exhibited an agerelated increase in adipogenic differentiation capacity and SA-βG expression. In both groups, the cells induced in osteogenic medium showed increased OCN expression and ALP activation, and the increments were more obvious in group A. Conclusion Human PDLSCs can be isolated from periodontal ligament tissues even from donors of advanced ages, but their proliferative and differentiation capacity decreases and their adipogenic differentiation capacity increases with age.