The efficacy of mindfulness‐based interventions for post‐traumatic stress disorder has not been demonstrated clearly nor have processes of change been examined extensively in the context of post‐traumatic stress. Decreases in trauma‐related rumination is one possible mechanism underlying the positive effect of mindfulness on reducing post‐trauma symptomatology. The present study investigated whether brief mindfulness training reduced post‐traumatic intrusions, testing the mediating role of trauma‐related rumination. Sixty female university students viewed a film clip depicting scenes of physical and sexual violence. They then listened to a short audio of either a mindfulness or relaxation exercise and were instructed to use the respective techniques to manage film‐related rumination in‐session and over the following week. The mindfulness induction decreased vividness of intrusions, but not intrusion frequency or associated distress, nor post‐traumatic stress symptoms or film‐related rumination. No mediation of film‐related rumination was found. Preliminary evidence was found for the effect of mindfulness training on reducing vividness of trauma intrusions, but not intrusion frequency or associated distress. However, the current study failed to observe increases in mindfulness following brief training. Despite this, trait mindfulness predicted lower levels of post‐traumatic stress symptoms. Future research should examine whether trauma‐related rumination constitutes a process of change using more intensive training of mindfulness‐based interventions for post‐traumatic stress disorder. Theoretical and clinical implications are discussed.