Ingredient analysis and the medical action of various teas are accomplished on multi angle. However, the research regarding the prevention and a treatment of oral cavity disease, which use the green tea, is still insufficient relatively. In this experiment, the virtue of green tea bag on periodontal disease was studied. This experiment was used in 11 beagles. As a test group, 6 beagles were rinsed their tooth with green tea bag. The remaining 5 beagles were rinsed with filter paper which was soaked with normal saline. The test found no statistical significance in gingival index, plaque index, calculus index and dental pocket depth. But the number of bacteria colonies decreased significantly in test groups. The periodontal disease is related to the number of bacterial colonies. Therefore, this results show that the green tea bag is effective for periodontal disease.