Prospective memory (PM) is the accurate execution of an intention in the future. PM may be negatively impacted by negative affect, but the underlying mechanisms remain unclear. Rumination may increase the frequency of task-irrelevant thoughts, which deplete attentional capacity and reduce performance. To date, no studies have examined state and trait rumination on an online measure of PM. The present study examined the effects of state and trait rumination on an event-based, focal PM task embedded within a one-back task over (...) multiple sessions. 95 non-depressed adults (18–53 years) completed measures of state/trait rumination, mood, and PM on at least two occasions. Using multi-level modelling, we found that a derived measure of trait rumination, but not an established trait rumination survey, nor negative mood, predicted poorer PM accuracy. These novel findings demonstrate that trait rumination may partially underlie the association between negative affect & PM in a non-clinical sample, and highlight the potential of online methods to study PM. (shrink)