Charities are encountering an unprecedented crisis during the Covid-19 pandemic. Most of the charities have moved their service on social media to reach more potential supporters, and thus charity’s online marketing-oriented strategies need more theoretical guidance. The present study aims to examine millennials’ motivations and affective stimuli to online and offline charitable support by using three aggregated levels of Self-Determination Theory (SDT): controlled motivation, autonomous extrinsic motivation, and autonomous intrinsic motivation. Besides, self/other benefits and local/global charities’ Facebook appeals were presented to explore the moderative effects on the relationship between SDT regulations and charitable support intention. The key finding is that millennials in the self-condition are more likely to show offline support with increasing autonomous extrinsic and intrinsic motivation whereas those in others-condition show decreased online and offline support intention with increasing controlled motivation. The result highlighted the stronger relation between autonomous extrinsic motivation and charitable support, indicating that the value, goals, and the practical meaning of charity events, compared to interest and pleasure (intrinsic motivation), better predict millennials’ charitable support. However, we didn’t find any moderative effects of local/global conditions.