With the increasing urgency of environmental degradation, it is crucial to investigate whether and why individuals from different socioeconomic statuses (SES) engage in environmental donations within social contexts to develop targeted strategies that promote environmental sustainability. However, the psychological mechanisms and neural activities underlying environmental donations across SES in social contexts remain unclear. The current study randomly assigned participants to high (low) SES groups and asked them to complete the environmental donation task in the (non) observable contexts while the electroencephalogram was recorded. Behaviorally, this study revealed that the presence of others promoted environmental donations in the low-cost condition and the average donations and acceptance rates were influenced by costliness. The ERP results indicated that high-SES individuals exhibited more negative N2 in the observable condition than in the non-observable condition. At the later stage, social observation modulated the neural activity evoked by donation decision making, with high-SES individuals showing larger P3 and late positive potentials (LPP) in the observable (vs. non-observable) condition. These findings suggest that public service institutions can implement targeted fundraising strategies that consider motivational differences among individuals with different SES, such as creating cost-effective environmental scenarios for low-SES individuals and designing reputation-enhancing situations for high-SES individuals.