This study assessed the incremental impact of performing acts of kindness, beyond the benefits seen from providing a resource booklet on stress management (that is available to all students at the host institution) with regard to the affect, social interaction anxiety, and mood of undergraduate students. This repeated-measures mixed methods study involved 69 full-time undergraduate students allocated to the intervention (kindness + stress booklet; n = 35) or comparator (stress booklet; n = 34) condition. The Brief Mood Introspection Scale, the International-Positive and Negative Affect Schedule-Short Form, and the Social Interaction Anxiety Scale-Straightforward were administered at pre-and immediate post-intervention. Inductive content analysis was performed on open-ended questions exploring participants' experiences with the study. No statistically significant results were found. Several themes highlighted self-perceived improvements in the wellbeing of intervention group participants. This study was perceived as a positive experience by many participants and demonstrated promise for a larger-scale university-based intervention. Keywords Kindness. Social interaction anxiety. Mood. Affect. Undergraduate students In recent years, the mental health of post-secondary students has been increasingly recognized as critical to understand (Auerbach et al. 2016; Blanco et al. 2008; Bruffaerts et al. 2018). This may, in part, be due to the many mental health issues that develop during young adulthood (Gibbons et al. 2018). In fact, some researchers