PURPOSE: To investigate the effect of carbohydrate and protein supplementation on mood, affect and discomfort perception during endurance exercise. METHODS:Ten well trained, healthy Chinese males (Age: 27.33±4.40 yr, height: 172.89±3.86 cm, weight: 63.50±5.12 kg, body fat percentage: 8.97±4.30 %, VO2max: 62.93±5.66 ml•kg-1•min-1) participated in the study with a double-blind counterbalance crossover design. Three types of nutritional treatments were implemented in three trials: 1) CHO+PRO: CHO-electrolyte solution (6.6% CHO, 26mg•L Na+, 8mg•L K+) with 24g whey protein isolate; 2) CHO-electrolyte solution (6.6% CHO, 26mg/L Na+, 8mg•L K+) with 24g sugar; 3) Sweetened electrolyte solution (26mg•L Na+, 8mg•L K+). All of the treatments were matched in sweetness with a zero-calorie sweetener and 5ml•kg was ingested before exercise and 2m•kg ingested every 15 minutes during exercise. The Chinese version of 24-item Brunel Mood Scale (BRUMS), Rating of Perceived Exertion (RPE), Pain intensity scale, Felt Arousal Scale (FAS) and Feeling Scale (FS) were applied in this study. Gas analysis was conducted every 30 minutes. Three-way ANOVA (time x treatment x stage) were applied for comparing the difference among treatments and time point. RESULTS:Blood glucose in CHO+PRO was higher than in the control group (5.35±0.81 vs. 4.45±1.03 mmol•L, P<0.05) at 90 min. RPE, FAS and pain intensity scale increased along with time; no difference was found among treatments. There was no difference among scores of dimensions in Depression, Anger, Confusion, Fatigue, Tension and Vigor among different time points of exercise. However, the score of Vigor dimension in CHO+CHO is higher than two other groups (2.10±2.07 vs. 4.10±1.52 vs.2.40±2.27, P<0.05). CONCLUSIONS:Exercise could induce a higher level of arousal, muscle pain and perceived exertion; however, pleasure-displeasure and the overall mood state were not affected. Ingestion of CHO+PRO drink did not induce stomach discomfort and overall mood disturbance during exercise, compared with CHO+CHO or placebo drink. In comparison with CHO+PRO, positive mood of Vigor could stay higher after ingesting an energy-matched amount of CHO in the present study.