Mindfulness is a state of paying conscious and nonjudgmental attention to present-moment experiences. Previous research relates this state to more effective emotion regulation and less emotion reactivity. We therefore hypothesized an attenuating effect of a mindfulness exercise on moral reactions that usually results from a bad conscience when having caused harm. Across five studies, we experimentally induced mindfulness via a short breathing exercise and then assessed harm-based moral reactions. As hypothesized, participants in the mindfulness (vs. control) exercise condition showed (i) attenuated repair intentions after having read a scenario in which participants caused harm to a friend (Study 3) and (ii) attenuated intentions to change harm-causing eating habits (Study 4). Results of Studies 1, 2 and 5 did not provide evidence for our hypothesis. A following meta-analysis across all five studies yielded an overall significant effect of mindfulness in the harm-condition, providing preliminary evidence for a potential downside to mindfulness.