Objectives <p>Guilt arises when an individual’s actions cause harm to others, leading not only to prosocial compensation, but also to detrimental self-punishment. Mindfulness can effectively ameliorate negative emotions and is related to lower guilt level and less compensatory behavior. Therefore, two studies were conducted to examine whether mindfulness would reduce guilt and self-punishment from the perspective of the Dual-mode Model of Mindful Emotion Regulation (D-MER).</p> Method <p>Across both studies, a dot-estimation task was used to induce varying levels of guilt in participants while different mindfulness strategies were applied. Study 1 (<i>n</i> = 34) investigated the effect of the mindful attention or immersion strategy on guilt and self-punishment using a within-subjects design. Study 2 (<i>n</i> = 75) investigated the effect of the mindfulness breathing or mind-wandering strategy using a mixed design in which strategies were employed before the dot-estimation task.</p> Results <p>In study 1, mindful attention significantly reduced guilt ratings and self-punishment behavior. In study 2, no significant differences in guilt or self-punishment were observed between the mindfulness breathing and mind-wandering groups, although the mindfulness group reported an increased present-focused awareness. Across the two studies, guilt was positively correlated with self-punishment.</p> Conclusions <p>Mindfulness can regulate moral emotions and behaviors when implemented actively as a regulatory strategy, but it would be less effective when delivered as a preventive strategy. Furthermore, the implications for moral emotion regulation and mindfulness interventions are discussed.</p> Preregistration <p>This study is not preregistered.</p>