The purpose of this study was to compare effects of different amounts of carbohydrate (CHO) in beverage on plasma glucose (GLU) concentration during exercise after feeding breakfast. Seven healthy Japanese male subjects performed 30-min cycling at an intensity on the 75% of maximal load at 3-h after feeding breakfast under 3 types of CHO (0 g, 30 g and 150 g) beverage conditions. The subjects ingested 500 mL of beverage dissolved each amount of glucose at 30-min before the exercise. The GLU concentrations were measured at 35- and 10-min before the exercise and every 5-min during the exercise. The minimum GLU concentrations under the 30 g condition for all subjects were lower than a criterion for hypoglycemic (72 mg / dL). The mean value also fell below the criterion at from 10- to 20-min during exercise. The minimum GLU concentration under the 150 g condition of only one subject was lower than the criterion, but the mean value did not fall below the criterion. Significant negative correlations were found between the subjects’ maximum oxygen uptake (VO2max) and the decreases in GLU concentration from maximum to minimum under both the 30 g (r = -0.947, p < 0.01) and 150 g conditions (r = -0.884, p < 0.01). This study clarified that feeding breakfast at 3-h before the exercise followed by the 30 g CHO beverage ingestion at 30 min before the exercise induced exercise-induced hypoglycemia, and that the subjects with higher VO2max had the greater decreases in GLU concentration.