Purpose: To investigate the protective effect of bisleuconothine A on periodontal tissue in rats and the mechanism involved. Methods: Adult male Sprague Dawley rats (n = 32) weighing 180 - 200 g (mean weight, 190 ± 10 g) were randomly assigned to four groups of eight rats each: control group, periodontitis group, bisleuconothine A (50 mg/kg) group and bisleuconothine A (100 mg/kg) group. Rats in the treatment groups received bisleuconothine intraperitoneally for two weeks. Periodontitis was induced in the rats using standard procedures. Serum and tissue samples were used for biochemical analysis. Alveolar bone loss was measured in rat maxillae, while the activity of bone alkaline phosphatase (BALP) was determined in serum. Tumor necrosis factor α (TNF-α) interleukin-1β and interleukin-6 (IL-1β and IL-6) were determined in gingival tissue using enzyme-linked immunosorbent assay (ELISA) kit. Gene and protein expressions of receptor activator of nuclear factor kappa-Β ligand (RANKL), osteoprotegerin (OPG), and matrix metallopeptidase-9 (MMP-9) were measured in gingival tissue using real-time quantitative polymerase chain reaction (qRT-PCR) and Western blotting, respectively. Results: Bisleuconothine A treatment significantly and dose-dependently reduced alveolar bone loss, as well as serum levels of TNF-α, IL-1β and IL-6, but increased BALP activity in periodontitis rats (p < 0.05). It also significantly and dose-dependently reduced mRNA expressions of RANKL and MMP-9, but significantly increased OPG mRNA expression (p < 0.05). Similarly, treatment with bisleuconothine A significantly and dose-dependently down-regulated RANKL, p-NF-kB, p-IkBα and iNOS proteins in gingival tissue of periodontitis rats (p < 0.05). The results of histopathological examination indicated that bisleuconothine A treatment significantly reversed histological changes in periodontal tissues of periodontitis rats. It also significantly reduced the degree of polymorphonuclear (PMN) cell infiltration in periodontal tissue. Conclusion: The results obtained show that bisleuconothine A protects periodontal tissue via the regulation of RANKL expression and infiltration of inflammatory cells. © Pharmacotherapy Group, Faculty of Pharmacy, University of Benin, Benin City, 300001 Nigeria.