OBJECTIVES: Research has shown that mindfulness in athletes is associated with positive outcomes. We therefore assessed the effect of mindfulness training on increasing mental toughness (MT) and psychological well-being (PWB). METHODS: This was a parallel-group, pre-and post-test, randomised controlled pilot trial. Forty-five female athletes from Iranian universities in Tehran were randomly assigned into experimental (n = 23) and control groups (n = 22). Forty-two completed the trial. The mindfulness training group received the Mindfulness-Acceptance-Commitment programme for 7 weeks. All subjects completed the Mindfulness Inventory for Sport (MIS), Sports Mental Toughness Questionnaire and PWB Scale. Data were analysed using mixed analysis of variance. RESULTS: Mindfulness training increased mindfulness in the experimental group (p < 0.01). In turn, increased mindfulness led to increased MT and PWB at 2-month follow-up (p < 0.05). CONCLUSIONS: Given that mindfulness training may increase the MT and PWB of athletes, these techniques should be considered for inclusion in sports coaching.