In a recent randomized controlled trial, couples participating in a mindfulness-based relationship enhancement program demonstrated significant improvements in relationship satisfaction and relationship distress (Carson, Carson, Gil, & Baucom, 2004). Here we report on a multiple mediation analysis of these couples’ improvements. Potential mediators included measures of couples’ engagement in exciting self-expanding activities, couples’ ability to accept one another’s difficult characteristics, and individual partners’ ability to relax. Results indicate that to a large extent, the mindfulness-related relationship improvements can be attributed to partners’ sense that they were participating in exciting self-expanding activities together during the course of the intervention. The implications of these findings for future mindfulness research are discussed.