Purpose: High-intensity continuous exercise is proposed to evoke unpleasant sensations as predicted by the dual mode theory (DMT), and may negatively impact on future exercise adherence. Previous studies support unpleasant sensations in affective responses during continuous high-intensity exercise, but the affect experience during high-intensity interval exercise (HIIE) involving brief bursts of high-intensity exercise separated by low-intensity activity is poorly understood in adolescents. We examined the acute affective, enjoyment and perceived exertion responses to HIIE compared to moderate-intensity interval exercise (MIIE) in adolescents. Methods: Thirteen adolescent boys (mean±SD; age 14.0±0.5 years) performed two counterbalanced exercise conditions: 1) HIIE: 8 x 1-minute work intervals at 90% maximal aerobic speed; and 2) MIIE: between 9-12 x 1-minute work intervals at 90% ventilatory threshold where the number of intervals performed were distance-matched to HIIE. HIIE and MIIE intervals were interspersed with 75 s active recovery at 4 km·h-1. Affect, enjoyment and rating of perceived exertion (RPE) were recorded before, during and after exercise. Results: Affect responses declined in both conditions but the fall was greater in HIIE than MIIE (P<0.025, ES=0.64 to 0.81). Affect remained positive at the end work-interval for both conditions (MIIE= 2.62±1.50; HIIE= 1.15±2.08 on feeling scale). No enjoyment differences were evident during HIIE and MIIE (P=0.32), but HIIE elicited greater post-exercise enjoyment compared to MIIE (P=0.01, ES=0.47). RPE was significantly higher during HIIE than MIIE across all work-intervals (all P<0.03, ES>0.64). Conclusions: Despite elevated RPE, HIIE did not elicit prominent unpleasant feelings as predicted by DMT and was associated with greater post-exercise enjoyment responses than MIIE. This study demonstrates the feasibility of the application of HIIE as an alternative form of PA in adolescents.