The aim of this study was to assess the relationship between trait mindfulness and mood and to examine whether the relationship is mediated by mind wandering. Eighty-two individuals (M age=24.27 years, SD=5.64, 18 men, 22%) completed a series of measures including the Five-Facet Mindfulness Questionnaire, the Profile of Mood States Questionnaire, and Meditation Breath Attention Exercise. Results showed that the level of mindfulness was significantly correlated with positive and negative mood, and the association between mindfulness and negative mood was mediated by mind wandering. This study indicated the important role of mind wandering in the relation between mindfulness and negative mood. Limitations and future research directions are discussed.