Whereas much research has demonstrated the effects of mindfulness-based interventions on emotional well-being, less work has examined the effects of mindfulness training on affect dynamics, referring to the dynamic processes through which affect fluctuates in daily life. The present study investigated the effects of a mindfulness-based stress reduction program (MBSR) versus an active control condition (music therapy stress reduction, MTSR) on several indicators of affect dynamics, namely affect variability, affect instability, and affect inertia, and difficulties with emotion regulation in a Chinese adult sample based in Singapore. One hundred and fifty-eight participants were recruited and randomly assigned to receive MBSR or MTSR. Participants completed a battery of questionnaires, followed by 3 days of ecological momentary assessment (EMA) measuring a variety of emotions at pre- and post-intervention. Of these participants, 121 provided baseline EMA data. Intent-to-treat analyses (n = 121) indicated that participants in the MBSR condition showed significantly greater decreases in variability (p < .001) and instability of negative affect (p < .001), and emotion regulation difficulties (p = .040) compared to the MTSR group. No between-condition differences were found on changes in affect inertia and any of the affect dynamic indicators for positive emotions. The study suggests that MBSR may have a unique impact on dynamics of negative, as opposed to positive emotions. The findings lend further support to the role of mindfulness training in facilitating effective regulation of negative emotions in the context of everyday life.