Purpose: Periodontitis is characterised by inflammation of periodontium and alveolar bone loss. Gardenia jasminoides is reported to have anti-inflammatory effects. In this study, we investigated the effects of aqueous extract of G. jasminoides (GJ) on periodontitis. Materials and Methods: Male Sprague-Dawley rats aged 7 weeks were randomly placed in three groups (n = 7); non-ligatured and non-treated (NL group), ligatured and distilled water-treated (L group) and ligatured and 100 mg/kg GJ-treated (GJ group). After oral administration of GJ for 14 days, the mandibles were removed for histology. In addition, RAW 264.7 cells were treated with 100 ng/ml receptor activator of nuclear factor-κΒ ligand (RANKL) and 1, 10 and 100 μg/ml GJ for 7 days to analyse the expression of periodontitis-related factors. Results: In GJ-treated mice, the score of alveolar bone loss was statistically significantly attenuated compared with the L group. GJ treatment showed inhibition effect in the progress of cementum demineralisation. The expressions of proinflammatory cytokines in gingival tissue were statistically significantly regulated by GJ treatment. Additionally, GJ treatment showed the dose-dependent inhibition of RANKL-induced osteoclast formation. Furthermore, GJ treatment downregulated the RANKL-induced cytokine production in RAW 264.7 cells. Conclusion: In summary, GJ ameliorated periodontitis-induced alveolar bone loss via inhibiting transcription factors including nuclear factor-κB, c-fos and extracellular signal-regulated kinase signalling. Therefore, GJ might be a therapeutic option for treating periodontitis. Keywords: periodontitis, Gardenia jasminoides, alveolar bone loss, osteoclasts