Relationship conflict often incites fears of rejection, and rejection fears can lead to destructive behaviors toward intimate partners. In the current study, we tested whether dispositional mindfulness attenuated rejection fears, and destructive behaviors arising from rejection fears, during daily conflict with romantic partners. Participants first completed measures of dispositional mindfulness, self-esteem, relationship commitment, and self-control. Participants then reported their daily experiences of conflict with their romantic partner, fears of rejection, and destructive behavior each day for 10 days. Greater daily conflict was associated with increases in daily rejection fears, and greater rejection fears were associated with increases in destructive behaviors. However, both of these within-person associations were attenuated for people higher in dispositional mindfulness. Moreover, the buffering effect of mindfulness on rejection fears was particularly effective for those low in self-esteem who chronically doubt their relational value and typically show heightened fears of rejection. The attenuating effect of mindfulness on rejection fears and destructive behaviors was also independent of other factors shown to produce more constructive reactions to relationship conflict, including participants’ relationship commitment and self-control. These results reveal the unique and important role dispositional mindfulness plays in regulating rejection fears and facilitating more constructive behaviors during daily life.