Because depressive symptoms are momentarily associated with lower levels of participation poststroke, it is crucial to investigate what moderates such associations to identify a potential intervention target to reduce the momentary links between depressive symptoms and participation poststroke. Self-regulation seems to be a potential moderator of such associations. To investigate the extent to which difficulties in self-regulation moderate the momentary associations between depressive symptoms and participation poststroke. This study uses a real-time, repeated-measures design using smartphone-based ecological momentary assessment surveys five times a day for 10 days. We performed multilevel modeling to uncover the momentary associations among the study variables. Community. 39 people with stroke. We obtained real-time data for difficulties in self-regulation (total, cognitive, behavioral, and emotion regulation), depressive symptoms, and participation in daily activities (performance in daily activities and satisfaction with performing daily activities). We included 1,612 survey responses in the analysis. Higher depressive symptoms were momentarily associated with lower levels of performance (β = -0.05 to -0.07, p < .001) and satisfaction (β = -0.04 to -0.06, p < .05), regardless of adjusting for self-regulation variables and other covariates. Difficulties in total self-regulation (β = -0.01, p < .001) and emotion regulation (β = -0.02, p < .001) magnified the negative associations between depressive symptoms and satisfaction with performing daily activities. Using self-regulation and emotion regulation strategies may be a target for just-in-time intervention for reducing the momentary associations between depressive symptoms and satisfaction with performing daily activities poststroke. Plain-Language Summary: Depressive symptoms have immediate and real-time associations with lower levels of participation in daily activities in people with stroke. Self-regulation, including cognitive regulation (e.g., goal setting, planning strategies), behavioral regulation (e.g., controlling impulsive behaviors), and emotion regulation (e.g., managing negative feelings), may be an intervention target for reducing the immediate associations between depressive symptoms and lower levels of participation poststroke. Thus, we investigated whether difficulties in self-regulation variables magnify the negative real-time associations between depressive symptoms and participation poststroke. To obtain real-time data on difficulties in self-regulation variables, depressive symptoms, and participation (i.e., performance and satisfaction), we asked 39 community-dwelling people with stroke to answer smartphone surveys. The results showed that difficulties in total self-regulation and emotion regulation magnified the negative associations between depressive symptoms and satisfaction with performing daily activities. Our findings suggest that self-regulation and emotion regulation strategies may be a target for real-time intervention for reducing the momentary associations between depressive symptoms and satisfaction with performing daily activities poststroke.