The social impact of observing others' charitable donations remains underexplored, with few studies examining the influence of donors' social class. Across three experiments, we investigated how the donor social class-donation type interaction influences the observers' perceived sacrificial costs or desire for a moral self-identity, which consequently affects their willingness to donate. The participants perceived higher costs when lower-class donors made monetary donations, but for time donations, they saw no difference in sacrificial costs by donor social class. Moreover, when the hourly wage was emphasized, the participants felt an increased desire for a moral self-identity from higher-class donors' monetary donations and became more willing to donate their money. These findings highlight the importance of considering both the donor social class and donation type when designing donation campaigns, and offer valuable insights for enhancing overall donation amounts.