Resumo. ABSTRACT The increased prevalence of obesity has endangered the health of Brazilian adolescents. Regular physical activity and lifestyle changes are recommended as prevention and treatment. However, there is no consensus on the dose-response of training programs. This study aimed at assessing the effectiveness of a high-intensity interval training program in aquatic environment (HIITAQ) on physical fitness and cardiometabolic risk factors in obese teenagers. The sample consisted of 18 adolescents of both sexes, aged 12 to 17 years, diagnosed with obesity. Anthropometric variables, physical fitness, blood glucose, and lipid profile were evaluated before and after 12 weeks of training. The program consisted of two sets of 4-8 repetitions for 30 seconds (85%-95% of maximal heart rate) and 60 seconds of active rest interval. After applying the program, a reduction in body mass index was seen, that is, BMI z-score (p <0.01), as well as a reduction of Total Cholesterol, TC (p <0.01), and LDL (p <0.01). There was an increase in basal metabolic rate (p <0.01) and peak VO2 (p <0.01). No differences were seen after the training with regard to fat percentage, body mass index (BMI) waist/height ratio (WHtR), fasting blood glucose, insulin, and HDL-c (p>0.05). The high-intensity training program in aquatic environment was effective in reducing cardiometabolic risk factors.