Based on self-determination theory, the current research aimed to explore the potential mediating effect of relatedness need satisfaction on the relationship between charitable behavior and well-being in the Chinese context. Employing a cross-sectional design, participants reported data on the aforementioned variables in Study 1. The results indicated that relatedness need satisfaction mediated the positive relationship between charitable behavior and hedonic well-being and that between charitable behavior and eudaimonic well-being. Subsequently, a field experiment was conducted in Study 2. Participants rated their levels of relatedness need satisfaction and well-being after charitable donation behaviors were primed. We again observed consistent results. Specifically, charitable behavior was positively associated with both hedonic and eudaimonic well-being, and these relationships were mediated by relatedness need satisfaction. The above findings help to clarify the association between charitable behavior and people's subjective feelings (i.e., well-being), and they deepen our understanding of the underlying mechanism from the perspective of psychological needs satisfaction.