Social exclusion significantly reduces prosocial behavior, as demonstrated in seven experiments. Participants who felt excluded donated less money, were less willing to volunteer, were less helpful after a mishap, and cooperated less in a mixed-motive game. The effect was mediated by empathy but not by mood, self-esteem, belongingness, trust, control, or self-awareness. Social exclusion temporarily impairs emotional responses, reducing the capacity for empathic understanding and thus undermining prosocial behavior. Prosocial behavior, which benefits others, is often costly to the self but is vital for social belonging. Social exclusion threatens this sense of belonging, reducing the motivation to perform prosocial acts. Exclusion may also impair inner responses necessary for prosocial behavior, leading individuals to prioritize self-preservation over helping others. Empathy, crucial for prosocial behavior, is reduced after exclusion, as the emotional system becomes temporarily inoperative. These findings suggest that social exclusion leads to a general decrease in prosocial behavior, as individuals become wary and less trusting of others. The results were consistent across different measures of prosocial behavior and manipulations of social exclusion. The effect size was large, with exclusion leading to a significant reduction in prosocial behavior. The findings highlight the importance of empathy in prosocial behavior and the negative impact of social exclusion on emotional and social functioning.Social exclusion significantly reduces prosocial behavior, as demonstrated in seven experiments. Participants who felt excluded donated less money, were less willing to volunteer, were less helpful after a mishap, and cooperated less in a mixed-motive game. The effect was mediated by empathy but not by mood, self-esteem, belongingness, trust, control, or self-awareness. Social exclusion temporarily impairs emotional responses, reducing the capacity for empathic understanding and thus undermining prosocial behavior. Prosocial behavior, which benefits others, is often costly to the self but is vital for social belonging. Social exclusion threatens this sense of belonging, reducing the motivation to perform prosocial acts. Exclusion may also impair inner responses necessary for prosocial behavior, leading individuals to prioritize self-preservation over helping others. Empathy, crucial for prosocial behavior, is reduced after exclusion, as the emotional system becomes temporarily inoperative. These findings suggest that social exclusion leads to a general decrease in prosocial behavior, as individuals become wary and less trusting of others. The results were consistent across different measures of prosocial behavior and manipulations of social exclusion. The effect size was large, with exclusion leading to a significant reduction in prosocial behavior. The findings highlight the importance of empathy in prosocial behavior and the negative impact of social exclusion on emotional and social functioning.