There are limited studies examining the effects of a mindfulness intervention for a specific sport population group. The aim of this applied study was to investigate the effects of a mindful sport performance enhancement (MSPE) program on the mindfulness and flow of adolescent swimmers. Sixteen competitive adolescent swimmers were split into MSPE (n = 9) and relaxation training (RT) (n = 7) groups for eight weeks. Participants completed measures of trait and state flow mindfulness pre and post intervention. Paired t test results revealed that the MSPE group improved trait flow characteristics and global trait flow. ANCOVA analysis also revealed significantly higher effects on global trait flow and the action-awareness merging and clear goals subscales for the MSPE group compared to the RT group. These results suggested that sport orientated mindfulness interventions can psychologically benefit competitive youth swimmers. The study indicates that further research could consider applied designs to investigate in more detail the experiences this population has with specific mindfulness exercises.