Introduction: Quercetin is a flavonoid found in a variety of plants, including guava, apples, onions, and tea. It’s been used as an anti-oxidant and anti-inflammatory substance for a long time. This study aims to investigate the effect of quercetin on periodontitis caused by Porphyromonas gingivalis-adhered ligatures. Methods: Eighteen male adult Sprague Dawley rats were divided into 3 groups, namely the control group (C, n=6) and the other two groups that received quercetin at 45mg/kg/day as a preventive (Qp, n=6) and a curative treatment (Qc, n=6), respectively. Under general anaesthesia, periodontitis was induced by placing a 3/0 non-resorbable sterile silk thread around the mandibular incisor teeth of eighteen male adult Sprague Dawley rats. The ligature placement caused severe irritation in the periodontal tissue. The animals were euthanized after 14 days of post-induction treatment, and samples of the mandibular portion were kept in formalin and prepared for histological processing to determine the grade of inflammation (GI). The periodontal pocket depth (PPD) was measured using the Michigan-O probe with Williams marks at the mesial and lingual sites of the rat’s incisors tooth to determine the clinical parameter. Results: Qp showed the best improvement, in both parameters, clinically (PPD score, p=0,0018 at the lingual site, and p=0,0264 at the mesial site) and histologically (GI, p=0,0002). Significant differences were found in preventing clinical attachment-loss statistically (p<0,05) on Qp, better than the Qc at an equal dose (p<0,05). Conclusion: This finding suggests that quercetin administered as a preventive measure (Qp) may promo