Porphyromonas gingivalis causes inflammation, and leads to the periodontitis in gingival tissue damage and bone resorption. Epigallocatechin-3-gallate (EGCG) is a major polyphenol extract from green tea with plenty of pharmacological functions. The aim of this study was to determine whether continuous oral intake of EGCG would alleviate P. gingivalis-induced periodontitis. Eight-week BALB/c mice were administered with EGCG (0.02%) or vehicle in drinking water. They were fed normal food and orally infected with P. gingivalis every 2 days, up to a total of 20 times, and then sacrificed at 15 weeks of age. The P. gingivalis-challenged group markedly increased alveolar bone resorption of the maxillae in BALB/c mice by Micro-CT detection, and administration of EGCG resulted in a significant reduction in bone loss. Inflammation cytokine antibody array and enzyme linked immunosorbent assay revealed that some inflammatory mediators in serum were increased by P. gingivalis infection, but were lowered after EGCG treatment. High positive areas of IL-17 and IL-1β in the gingival tissue were observed in the P. gingivalis-challenged mice, and were reduced by EGCG treatment. Real-time polymerase chain reaction (PCR) analyses also showed the expressions of IL-1β, IL-6, IL-17, IL-23, TNF-α and other mediators in gingival tissue were higher in P. gingivalis-challenged mice, and were down-regulated with EGCG treatment, except IL-23. Our results suggest that EGCG, as a natural healthy substance, probably alleviates P. gingivalis-induced periodontitis by anti-inflammatory effect.