To examine user experiences in a moderated Facebook group intervention aimed at Coronavirus disease 2019 (COVID-19) vaccine promotion. Facebook group members were given 2-3 vaccination posts/day for 28days (fourweeks). Posts were aimed at educating about COVID-19 vaccination, soliciting concerns around COVID-19 vaccination, and engaging members. Participants were surveyed about their experience at four weeks. Moderated Facebook group. Unvaccinated individuals who were randomized to the intervention group and completed fourweek follow-up (N = 216, 82.1%). After fourweeks, participants rated their experience in the Facebook group (eg, program satisfaction) and provided open-text responses about their satisfaction with the group. Free-text responses were dual coded and emergent themes were examined. On average, participants were 37.0 years old (SD = 10.3), majority female (70.9%), and white (79.7%). The majority of participants were satisfied with the group (76.7%), agreed that other people were friendly (M = 5.58/7), and felt safe discussing health information (M = 3.96/5). Open-text responses revealed that participants liked the program because they thought the information was useful (27.7%), other members were friendly (16.1%), and the group was a safe place (13.8%). While many responded that there was nothing they did not like about the program (37.6%), nearly one-third (31.9%) reported disliking the program because it appeared to be too much in favor of vaccination and because other members came across as rude (7.1%). Those with conservative political views were less likely to be satisfied with the group (P = .04). Facebook groups represent an acceptable way to engage participants to improve vaccination against COVID-19. Some aspects of the Facebook group could be improved for future iterations.