The purpose of this study was to evaluate the effectiveness of gargling solution with 0.05% NaF and 10% Xylitol in orthodontic patients with fixed appliance. The sample consisted of 30 adolescent patients who were classified into an experimental group and a control group, 15 patients each. Experimental group was used experimental gargling solution and the control group was used with placebo solution. The change of S. mutans in saliva was observed by Cariescreen^® SM kit at pre and post 2, 4, 6, 8 weeks. The results were as follows. 1. There were significant reduction in the number of S. mutans in saliva between pre and post 2 weeks(p<0.01), 4 weeks(p<0.05), 6 weeks(p<0001),, and 8 weeks(p<0001) in experimental group. And significant reduction also were observed in the number of Ss mutans in saliva between post 2 weeks, 6 weeks(p<0.05), and 8 weeks(p<0.05), but no significant reduction were showed in control group. 2. There were significant correlation in the number of S. mutans between each measurement time(pre and post 2, 4, 6, 8 weeks) in control group, 3. There we -e no correlation between pre and post 2 weeks, but significant correlation were observed between 2, 4, 6, 8 weeks in experimental group.