Objective <p>Reactive aggression is an impulsive reaction driven by anger and is believed to be reduced through mindfulness intervention in clinical and non-clinical samples. However, it is unclear why mindfulness intervention is effective. This study examined which dimension of mindfulness (acceptance and awareness) contributed to lower reactive aggression from trait and state perspectives.</p> Method <p>Study 1 explored the relationship between trait mindfulness and reactive aggression using the Taylor Aggression Paradigm (<i>n</i> = 116). Study 2 examined whether state acceptance or state awareness enhanced by distinct single 15-min practice sessions can reduce anger levels and reactive aggression (<i>n</i> = 189).</p> Results <p>The results showed that trait mindfulness, but not trait awareness, negatively correlated with anger and reactive aggression. The mindfulness group (<i>n</i> = 47) that received both awareness and acceptance guidance reported less anger and reactive aggression than the awareness group (that only received awareness guidance, <i>n</i> = 48), the relaxation group (<i>n</i> = 46), and the control group (<i>n</i> = 48), indicating significant between-group differences. Intervention types moderated the relationship between anger and reactive aggression; anger significantly and positively predicted reactive aggression in the control group, but not in the other three groups.</p> Conclusions <p>The results suggest that acceptance plays an essential role in mitigating aggressive reactions in provocative situations. Further, well-designed mindfulness training may be a promising intervention for reducing reactive aggression.</p> Preregistration <p>This study is not preregistered.</p>