Objectives: The present study examined the preliminary efficacy of an ultra-brief cognitive defusion intervention, compared to a positive self-affirmation intervention, on moderate subclinical Public Speaking Anxiety (PSA). Method: Sixty-three participants (M=25.70 yrs, SD=9.48) first completed a questionnaire assessing PSA symptomology and were then randomly assigned to receive one of two interventions (cognitive defusion, positive self-affirmation) or nothing at all (no-treatment control). All participants then performed an impromptu speech task before recompleting the questionnaire. Results: A significant decrease in PSA was reported within the cognitive defusion condition, relative to the positive self-affirmation and no-treatment control conditions. Conclusions: An ultra-brief cognitive defusion intervention has the potential to reduce short-term anxiety among those with moderate PSA.