This study aimed to clarify the effects of carbohydrate mouth rinse on exercise performance. We examined the effect of mouth rinse on fatigability. Thirty healthy male college students completed three trials with non mouth rinse (CON), mouth rinse intervention of 6% glucose (GMR), and artificial sweetener (PLA). Handgrip exercise was performed as a fatigue task. The subjects performed a 10-seconds maximal voluntary contraction (MVC) followed by a 40% MVC rhythmic grasping movement for 14 per minutes, followed by a 4-seconds rest. This set of exercises was performed for a total of ten sets. Mouth rinse was performed from the 5th set to the 10th set. The subjects were divided into three groups: L, M, and S, according to the degree of decrease in MVC due to fatigue in CON. The effect was evaluated using the rate of change in MVC after the mouth rinse. The evaluation was performed for each trail and group. In the L group, mouth rinse significantly improved the rate of change of MVC compared with the other trials (GMR vs. CON: P = 0.002; PLA vs. CON: P = 0.042). A significant trend was observed in the M (GMR vs. CON: P = 0.062), but not in the S. In conclusion, the effects of mouth rinse differed depending on fatigability in isometric hand grip performance, with mouth rinse inhibiting the decrease of motor fatigue. In addition, it was suggested that the sweetness of carbohydrates may have an effect on mouth rinse.