For the purpose of confirming the effectiveness of hainosankyuto against periodontitis, we induced periodontitis by treating carrageenin in the gingiva at the right mandibular first molar in the oral cavity of a rat. We administered 2900 mg/kg of hainosankyuto orally for 10 days, and then, examined the anti-inflammatory effect of hainosankyuto on periodontitis. The gingival condition was evaluated by photographing, and histopathological analysis was performed by pathological specimens of removed inflamed-sites after the final administration. As a result, swelling of the gingival was suppressed by hainosankyuto. The periodontal pockets became shallower. Erosion of the epithelial layer was improved. Extension of the epithelial process, decrease of inflammatory cells, and maturing of periodontal membrane were observed. In addition, decrease of the neutrophils, increase of blood vessels and decrease of the osteoclasts were also revealed by histopathological analysis. Furthermore, extension of the junctional epithelium leg and shortened distance of apical movement on junctional epithelium were observed. These results suggested that hainosankyuto would have an anti-inflammatory effect on periodontitis.