This study explores the impact of mindfulness meditation on anger. A meditation group (N = 37) attended 5-10 minutes of mindfulness meditation daily for a week. They were assessed with self-report scales measuring three aspects of anger (rumination, arousal, and lengthiness) before, just after, and four weeks after their one-week participation. Their scores were compared to a control group (N = 27), which was assessed at the same intervals as the meditation group. The meditation group was also asked to evaluate their current mood using the Affect Grid before and after each meditation. The results indicated that participants in the meditation group who continued meditation voluntarily after the week of their participation had decreased anger rumination scores just after and four weeks after their participation. Additionally, the pleasant score on the Affect Grid increased after meditation for almost all the participation days. These findings suggest the efficacy of mindfulness meditation on improving the tendency to ruminate about anger episodes in the medium term to long term, and also on improving mood in the short term.