Abstract: Objective：To evaluate the effects of Prevotella intermedia supernatant on the expression of receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) in human gingival fibroblasts (HGFs). Methods：The HGFs were treated with gradient Prevotella intermedia supernatant. HGFs were observed under the microscope. The real-time RT-PCR and Western blot analysis were used for testing the expression of RANKL and OPG, and the RANKL/OPG ratio was calculated. Results：The number of cells decreased with increase of the supernatant concentration. At 50 μg/mL, no cell survival could be observed under the microscope. The ratio of RANKL/OPG was increased in the cells treated with 12.5 μg/mL of Prevotella intermedia supernatant（P < 0.01）. Conclusions：Prevotella intermedia supernatant could disrupt the homeostasis of RANKL/OPG, destroy the microenvironment of osteoclast differentiation. Prevotella intermedia supernatant may play a regulatory role in osteoclast differentiation and bone resorption in periodontitis.