Ecological momentary assessment (EMA) is a method of data collection that entails prompting individuals to report their experiences (e.g., thoughts, feelings, and behaviors) in real time over the course of their day-to-day lives. By providing rich information about how these experiences unfold over time within an individual, EMA has the potential to substantially advance our understanding of grief. However, there is uncertainty about how bereaved adults will respond to EMA, especially among those with high prolonged grief symptom severity. Accordingly, we evaluated the feasibility and acceptability of an EMA protocol in bereaved adults with low and high prolonged grief severity. Participants completed six 12-item EMA surveys per day on their smartphones for 17 days. Adherence was high (mean survey completion = 90%, median = 96%), and only 6% of participants withdrew. Adherence remained high in those with high prolonged grief symptom severity (mean = 86%; median = 96%). On average, participants reported agreement that survey frequency and length were acceptable. There was no evidence for systematic worsening of symptoms during EMA data collection. Together, these findings suggest that EMA is feasible, acceptable, and safe for bereaved adults, including those with high prolonged grief symptom severity.