Past research reveals important connections between meditative practices and compassion. Most studies, however, focus on the effects of one type of meditation (vs. a no-intervention control) on a single expression of compassion (e.g. offering a seat) towards a relatable target (e.g. a person on crutches), without exploring possible mechanisms. Hence, few studies include different types of meditation, active controls, multiple ways to express compassion, unrelatable targets, and potential mediators. To this end, the present study compared the effects of mindfulness meditation with those of compassion meditation on different expressions of compassion towards a convicted murderer. Seventy-four participants were randomly assigned to a mindfulness meditation, compassion meditation, or active control class, or a no-class control. After an 8-week programme, we assessed compassion by giving participants the option of fulfilling a murderer’s request that they write him and then coding those letters for empathy, sympathy, forgiveness, and optimism. Participants in the compassion meditation class wrote more optimistic letters compared to participants in the other three conditions, in part because they valued positivity more. No statistically significant differences emerged for the other expressions of compassion. We discuss the implications of these findings for our understanding of how meditation increases compassion towards unrelatable targets.