The purpose of this study was to examine the association between greater engagement (i.e., number of times participated) in mindfulness exercises administered in large university lectures and students' writing self-efficacy. For eight weeks, a breathing exercise was administered to students in one lecture section, and a progressive muscle relaxation (PMR) exercise was administered to students in another lecture section of the same course. Participants (n = 147) completed measures of writing self-efficacy before (T1) and after (T2) the eight-week exercise period. Engagement was greater in the breathing exercise than in the PMR exercise (p < 0.05). Writing self-efficacy was marginally greater (p = 0.08) at T2 for those administered the breathing exercise than for those administered the PMR exercise. Correlational analyses further showed that engagement in the breathing exercise was associated with writing self-efficacy at T2 (p < 0.01), but engagement in the PMR exercise was not (p = 0.21). We conclude with implications for course instructors using mindfulness exercises to enhance desirable writing outcomes.