Anxiety sensitivity (AS) is the fear of arousal related sensations based on the belief that these sensations may have harmful or negative consequences, such as death, insanity, or social rejection (Reiss & McNally, 1985). Significant reductions in AS have been observed following as little as one session of moderate intensity exercise (Broman-Fulks et al., 2015); however, the effect of high intensity exercise on AS has not yet been investigated. Reductions in AS are associated with successful treatment outcomes in clinical populations, as well as a decreased risk of developing mental disorders in nonclinical populations (Schmidt, Keough, Timpano, & Richey, 2008). Treatments capable of reducing AS may have broad and important implications for the prevention and treatment of a range of mental disorders, especially the anxiety and mood disorders. This randomized controlled trial was designed to examine the effect of different levels of exercise intensity (i.e., moderate and high) on reductions in AS following a single session of exercise. A total of 56 participants attending an in-lab session were randomized into either a 10-minute sprint interval training group (SIT), a 50-minute moderate intensity continuous training group (MICT), or a waitlist control group. All participants completed self-report psychological measures, including a measure of AS, prior to and following completion of their assigned exercise session. Follow up measures were administered at 3 and 7 days after the in-lab session. Hierarchical linear modeling was used to evaluate whether the two exercise protocols were efficacious at reducing AS, symptoms of depression, intolerance of uncertainty, and distress intolerance, and if so, whether one protocol was more efficacious than the other. The results of this study show that although both protocols significantly reduced AS, effects were attributable to significant reductions across the different dimensions of AS. Specifically, for the SIT group, significant reductions in AS were observed only on the Physical Concerns subscale, but not on the Social or Cognitive Concerns subscales. Conversely, for the MICT group, significant reductions were only observed on the Social and Cognitive Concerns subscales, but not on the Physical Concerns subscale. Significant reductions in symptoms of depression, intolerance of uncertainty, and distress intolerance were not observed following either exercise protocol. The current trial is the first to present evidence regarding the effect of SIT on features of psychological wellbeing. Findings that SIT and MICT target different dimensions of AS could allow for increased flexibility when tailoring specific exercise recommendations to individuals. Additionally, given that lack of time is frequently reported as a barrier to exercising regularly (Trost, Owen, Bauman, Sallis, & Brown, 2002), findings that SIT reduces overall AS to a similar extent as MICT in a fraction of the time, could also assist the refinement of exercise strategies for improving psychological wellbeing and increasing overall exercise adherence. Keywords: randomized controlled trial, anxiety sensitivity, sprint interval training, moderate intensity continuous training, high intensity interval training