Cardiovascular diseases (CVD) account for ~ 1/3 of all deaths in the UK. Although the clinical manifestations of CVD are not present until later life, the atherosclerotic process has its origins in childhood. Postprandial lipaemia (PPL) and hypertension are independent risk factors of CVD and can be favourably modified with an acute bout of exercise in adults. A single bout of aerobic exercise (30-60 min) can attenuate PPL in adolescents. However, the majority of adolescents fail to reach the recommended 60 min of daily moderate to vigorous exercise. Time efficient, high-intensity interval exercise (HIIE) has recently been shown to be more effective than moderate intensity exercise (MIE) at reducing PPL in adults. The purpose of this study was to examine the effect of a single bout of HIIE and MIE on postprandial triacylglycerol (TAG), systolic blood pressure (SBP) and lipid oxidation in adolescents. Twenty adolescents (10 male, 14.3 ± 0.3 y) completed three 1-day trials on separate days: 1) rest (CON); 2) 8 x 1 min cycling at 90% peak power with 75 s recovery (HIIE); 3) cycling at 90% of the gas exchange threshold (MIE, which was work-matched to HIIE), one hour before consuming a high fat milkshake (1.50 g/kg fat, 80 kJ/kg). Postprandial TAG, SBP and fat oxidation (indirect calorimetry) were assessed over four hours. Differences between means were analysed using mixed model ANOVA (condition by sex) with follow up pair wise comparisons interpreted using the 95% confidence interval (CI) and effect size (ES). An ES of 0.2 was taken as the smallest worthwhile change between means. The incremental area under the curve (iAUC) for TAG was elevated in HIIE (10%, CI -0.14 to 0.56, ES=0.24) with no change in MIE (CI -0.30 to 0.37, ES=0.04) for boys. For girls, HIIE and MIE lowered iAUC-TAG by 34% (CI -1.43 to -0.17, ES=0.58) and 38% (CI -2.13 to 0.31, ES=0.73) respectively, with no difference between HIIE and MIE (CI -0.77 to 0.57, ES=0.14). Changes in TAG were not related to energy expenditure during exercise or postprandial fat oxidation (all r<0.2). Postprandial SBP (total-AUC pooled for both sexes) was lower in HIIE compared to both CON (CI -19 to -3, ES=0.68) and MIE (CI -15 to -2, ES=0.60), with no difference between MIE and CON (CI -8 to 4, ES=0.14). Postprandial lipid oxidation tAUC (pooled for both sexes) for HIIE was increased by 23% compared to CON (CI 0.04 to 0.12, ES=0.88) and 16% compared to MIE (CI 0.03 to 0.09, ES=0.66). Postprandial health outcomes are dependent on exercise intensity and sex when exercise is performed 1 hour prior to a high fat meal. Specifically, HIIE and MIE can meaningfully attenuate PPL in girls but not boys, but HIIE is more effective at lowering SBP and increasing lipid oxidation during the postprandial period. These findings support the use of HIIE as an effective alternative to MIE to improve postprandial health outcomes in adolescents.