Background: The 2020 Summer Olympics will be held in Tokyo, Japan where the heat and humid often reach 40°C and 70% relative humidity (RH) (1). Heat and humidity (H&H) have a substantial negative effect on exercise performance, however, exposure to H&H can lead to physiological adaptations (e.g. expanded plasma volume and sweat rate) can enhance exercise performance in both H&H and in ‘normal’ environmental conditions (2, 3). In highly trained endurance athletes, exercise induced acclimation can occur in as little as 5-days (known as short term heat acclimation, STHA) (4, 5). However, it is unknown if STHA can be achieved in different athletic populations such as elite amateur boxers. Aims: To examine the effects of a 5-day STHA protocol on cardiovascular performance, sweat loss, and hydration status in elite amateur boxers. Methods: 9 (3 female) elite level amateur boxers (mean ± SD: 22.5 ± 5.1 years, 179.1 ± 9.8 cm, 73.3 ± 20.5kg) underwent a 5-day STHA protocol. All sessions were conducted in an environmental chamber set at 32°C and 70% RH, during the same time of day, with a minimum of 3 hours post-prandial. Each session was 60 minutes in length which consisted of dynamic warm up, exercise (eight, 1-min intervals at 85% of heart rate max (HRmax) followed by 20-min steady-state at 75% HRmax)) conducted on a treadmill and cycle ergometer (alternated daily), cool down and stretch. Each session consisted of a pre-weight and urine specific gravity (USG) measurement with a post-session weigh out. Pre and post STHA protocol cardiovascular performance testing: 24 hours pre and post STHA, cardiovascular performance was assessed via repeat sprint assessment test in normal environmental conditions (22°C). Data were analyzed using a One-way ANOVA followed by post hoc t tests when appropriate with a priori value set at (p ≤ 0.05). Results: Data are absolute and change (△) pre-to-post STHA ± SD. Repeat sprint assessment significantly improved pre- to post-STHA ~ 44% (+△6 ± 6.9 more sprints completed, p = 0.02, d = 0.9). Daily sweat loss did not change significantly from Day 1-5 (p = 0.3), however, intra-day loss was significant (1.5 ± 1.5kg, △2%, p < 0.05). USG was significantly increased from Days 1-5 (1.0188 ± 0.0101 to 1.01453 ± 0.006, △-0.42%, p = 0.05, d = 0.54). Conclusion: 5-Day STHA in elite boxers significantly improved cardiovascular performance, hydration status, and increased intra-day sweat loss. These observations are indicative of positive physiological adaptations that improve exercise performance in H&H. Therefore, we conclude that a 5-Day STHA protocol can enhance physiological exercise responses in elite amateur boxers.