During a health crisis, prosocial sharing of health-related information (HRI) on social media can help to deliver early warnings about new diseases, raise social awareness, exchange support, and spread health policies. Current literature has mainly focused on the factors of general sharing of HRI under normal conditions but neglected those motivations under the health crisis context. This research aims to investigate factors that influence online users’ prosocial sharing of HRI during a health crisis. To obtain the objective, this study developed a dual helping-protecting motivation model from the fear appeal model and social exchange theory. The partial least squares analysis, carried out on the surveyed data of 326 participants, revealed that prosocial sharing intention is affected by protecting factors (i.e., sharing efficacy, response efficacy) and helping factors (i.e., reciprocity expectation). Additionally, both perceived health risk and perceived information quality risk were found to influence the sharing intention via motivational factors.