Grapefruit seed extract has been reported to have antimicrobial effect. The purpose of this study was to evaluate the antimicrobial and anti-gingivitis effect of chewing gum containing grapefruit seed extract and xylitol. 40 healthy subjects with gingivitis or early periodontitis were divided into two groups. Subjects in the experimental group chewed gum containing grapefruit seed extract and xylitol while subjects in the control group chewed gum containing only xylitol. All subjects received scaling and tooth brushing instruction. 1 week after scaling was set as baseline. Gingival index and plaque index were scored at baseline, 1 week, 2 week, 3 week and 4 week. Bleeding index, probing pocket depth and clinical attachment level were scored at baseline, 2 week and 4 week. The number of total bacteria and Streptococcus mutans in unstimulated saliva of experimental group were counted at 1 week, 2 week, 3 week and 4 week. Gingival indices of experimental group and control group at baseline, 1 week, 2 week, 3 week and 4 week were 0.850${pm}$0.298, 0.575${pm}$0.345, 0.533${pm}$0.332, 0.459${pm}$0.311, 0.408${pm}$0.224 and 0.758${pm}$0.379, 0.592${pm}$0.276, 0.563${pm}$0.281, 0.454${pm}$0.194, 0.413${pm}$0.199 (mean${pm}$SD), respectively. Plaque indices of experimental group and control group at baseline, 1 week. 2 week, 3 week and 4 week were 0.497${pm}$0.500, 0.375${pm}$0.484, 0.332${pm}$0.471, 0,286${pm}$0.452, 0.210${pm}$0.407 and 0.411${pm}$0.492, 0.375${pm}$0.484, 0.354${pm}$0.479, 0.313${pm}$0.463, 0.193${pm}$0.395, respectively. Bleeding indices of experimental group and control group at baseline, 2 week and 4 week were 0.377${pm}$0.177, 0.298${pm}$0.152, 0.192${pm}$0.108 and 0.383${pm}$0.124, 0.318${pm}$0.153, 0.225${pm}$0.126, respectively. Probing pocket depth of experimental group and control group at baseline, 2 week and 4 week were 2.56${pm}$1.00, 2.40${pm}$0.65, 2.23${pm}$0.64 and 2.45${pm}$0.682.37${pm}$0.57, 2.19${pm}$0.57, respectively. Clinical attachment level of experimental group and control group at baseline, 2 week and 4 week were 2.58${pm}$1.01, 2.43${pm}$0.67, 2.26${pm}$0.65 and 2.49${pm}$0.70, 2.40${pm}$0.59, 2.22${pm}$0.62, respectively. The % of reduction of total bacteria in saliva of experimental group at 2 week, 3 week and 4 week were 46 ${pm}$ 53%, 53 ${pm}$ 5% and 69 ${pm}$ 33%. The % of reduction of Streptococcus mutans count in saliva of experimental group at 2 week, 3 week and 4 week were 52${pm}$69%, 88${pm}$30% and 89${pm}$17%. From these findings, it can be concluded that regular use of grapefruit seed extract /xylitol chewing gum may be effective to control and prevent gingivitis and may have caries-preventive effect.