ObjectivesHigh levels of organisational citizenship behaviour can enable nurses to cooperate with coworkers effectively to provide a high quality of nursing care during the outbreak of COVID-19. However, the association between autonomy, optimism, work engagement and organisational citizenship behaviour remains largely unexplored. This study aimed to test if the effect of autonomy on organisational citizenship behaviour through the mediating effects of optimism and work engagement.Study designThis was a cross-sectional study.SettingThe study was conducted in the Wuhan Jinyintan Hospital in China.ParticipantsIn total, 242 nurses who came from multiple areas of China to work at the Wuhan Jinyintan hospital during the COVID-19 epidemic participated in this study.MethodsA serial mediation model (model 6) of the PROCESS macro in SPSS was adopted to test the hypotheses, and a 95% CI for the indirect effects was constructed by using Bootstrapping.ResultsThe autonomy–organisational citizenship behaviour relationship was mediated by optimism and work engagement, respectively. In addition, optimism and work engagement mediated this relationship serially.ConclusionThe findings of this study may have implications for improving organisational citizenship behaviour. The effects of optimism and work engagement suggest a potential mechanism of action for the autonomy–organisational citizenship behaviour linkage. A multifaceted intervention targeting organisational citizenship behaviour through optimism and work engagement may help improve the quality of nursing care among nurses supporting patients with COVID-19.