<p>Mindfulness-based art therapy (MBAT) is an interdisciplinary intervention that integrates mindfulness techniques with art activities. While previous research has examined MBAT’s effectiveness in reducing depressive symptoms, little is known about the temporal dynamics of change during participation. This study explored session-to-session changes in mindfulness, rumination, and affect among hospitalized patients with depressive episodes. The study involved 47 inpatients who participated in MBAT, including mindfulness techniques, mindful art exercises, and group discussions. Participants reported mindfulness, rumination, and emotions twice weekly using a diary method. Results indicated increased mindfulness and positive affect and decreased rumination and negative affect over time. However, contrary to expectations, changes in mindfulness did not predict later changes in rumination or affect. No evidence was found for reverse associations, meaning that changes in rumination or affect did not predict subsequent mindfulness. Instead, more time spent on mindfulness practice during home assignments was associated with reduced rumination, while time spent on art exercises was linked to improved emotional states. These findings suggest that mindfulness practice primarily targets cognitive patterns, such as repetitive negative thinking, while art-based activities regulate emotional states. Additionally, mindfulness, rumination, and affect exhibited oscillatory patterns, with greater fluctuations over longer time intervals and among participants with shorter therapy durations. These findings provide novel insights into the mechanisms of change in MBAT, emphasizing the importance of balancing mindfulness and art-based exercises to optimize therapeutic outcomes. Future research should explore how sequencing and integration of these components affect intervention effectiveness.</p>